diff --git a/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumModel.java b/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumModel.java
index ac7bb1c04..37e90db93 100644
--- a/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumModel.java
+++ b/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumModel.java
@@ -10,6 +10,7 @@
 import io.vertx.codegen.type.TypeMirrorFactory;
 
 import javax.annotation.processing.ProcessingEnvironment;
+import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ElementKind;
 import javax.lang.model.element.TypeElement;
@@ -17,6 +18,7 @@
 import javax.lang.model.type.TypeMirror;
 import javax.lang.model.util.Elements;
 import javax.lang.model.util.Types;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -85,7 +87,12 @@ public boolean process() {
               enumItemDeprecatedDesc = new Text(Helper.normalizeWhitespaces(methodDeprecatedTag.get().getValue())).map(Token.tagMapper(elementUtils, typeUtils, modelElt));
             }
           }
-          return new EnumValueInfo(elt.getSimpleName().toString(), doc, elt.getAnnotation(Deprecated.class) != null, enumItemDeprecatedDesc);
+          List<? extends AnnotationMirror> annotationMirrors = elt.getAnnotationMirrors();
+          List<AnnotationValueInfo> annotationValueInfos = new ArrayList<>();
+          if (annotationMirrors != null) {
+            annotationMirrors.stream().map(annotationValueInfoFactory::processAnnotation).forEach(annotationValueInfos::add);
+          }
+          return new EnumValueInfo(elt.getSimpleName().toString(), doc, elt.getAnnotation(Deprecated.class) != null, enumItemDeprecatedDesc, annotationValueInfos);
         }).
         collect(Collectors.toList());
       if (values.isEmpty()) {
diff --git a/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumValueInfo.java b/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumValueInfo.java
index 823b7ab37..8f758fc24 100644
--- a/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumValueInfo.java
+++ b/vertx-codegen-processor/src/main/java/io/vertx/codegen/EnumValueInfo.java
@@ -2,6 +2,12 @@
 
 import io.vertx.codegen.doc.Doc;
 import io.vertx.codegen.doc.Text;
+import io.vertx.codegen.type.AnnotationValueInfo;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
 /**
  * The value (member) of an enumeration model.
@@ -14,12 +20,14 @@ public class EnumValueInfo {
   private final Doc doc;
   private final boolean deprecated;
   private final Text deprecatedDesc;
+  private final Map<String, AnnotationValueInfo> annotations;
 
-  public EnumValueInfo(String identifier, Doc doc, boolean deprecated, Text deprecatedDesc) {
+  public EnumValueInfo(String identifier, Doc doc, boolean deprecated, Text deprecatedDesc, List<AnnotationValueInfo> annotations) {
     this.identifier = identifier;
     this.doc = doc;
     this.deprecated = deprecated;
     this.deprecatedDesc = deprecatedDesc;
+    this.annotations = annotations.stream().collect(HashMap::new, (m, a) -> m.put(a.getName(), a), HashMap::putAll);
   }
 
   /**
@@ -48,4 +56,20 @@ public boolean isDeprecated() {
   public Text getDeprecatedDesc() {
     return deprecatedDesc;
   }
+
+  /**
+   * @return the list of {@link AnnotationValueInfo} for this enum value
+   */
+  public List<AnnotationValueInfo> getAnnotations() {
+    return new ArrayList<>(annotations.values());
+  }
+
+  /**
+   * @param annotationName fully qualified name of an annotation type
+   * @return {@link AnnotationValueInfo} for an annotation of given type present on this enum value,
+   * or {@code null} if an annotation of given type is not present on this enum value
+   */
+  public AnnotationValueInfo getAnnotation(String annotationName) {
+    return annotations.get(annotationName);
+  }
 }
diff --git a/vertx-codegen-processor/src/main/java/io/vertx/codegen/Model.java b/vertx-codegen-processor/src/main/java/io/vertx/codegen/Model.java
index e0f1daeb4..1387e398c 100644
--- a/vertx-codegen-processor/src/main/java/io/vertx/codegen/Model.java
+++ b/vertx-codegen-processor/src/main/java/io/vertx/codegen/Model.java
@@ -4,10 +4,12 @@
 import io.vertx.codegen.type.TypeInfo;
 
 import javax.lang.model.element.Element;
+import java.lang.annotation.Annotation;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 
 /**
  * @author <a href="mailto:julien@julienviet.com">Julien Viet</a>
@@ -26,6 +28,16 @@ default List<AnnotationValueInfo> getAnnotations() {
     return Collections.emptyList();
   }
 
+  default Optional<AnnotationValueInfo> getAnnotation(Class<? extends Annotation> annotationType) {
+    String annotationName = annotationType.getName();
+    for (AnnotationValueInfo annotation : getAnnotations()) {
+      if (annotation.getName().equals(annotationName)) {
+        return Optional.of(annotation);
+      }
+    }
+    return Optional.empty();
+  }
+
   default Map<String, Object> getVars() {
     HashMap<String, Object> vars = new HashMap<>();
     vars.put("helper", new Helper());
diff --git a/vertx-codegen-processor/src/main/java/io/vertx/codegen/PropertyInfo.java b/vertx-codegen-processor/src/main/java/io/vertx/codegen/PropertyInfo.java
index 1711e8c10..4fc37ad71 100644
--- a/vertx-codegen-processor/src/main/java/io/vertx/codegen/PropertyInfo.java
+++ b/vertx-codegen-processor/src/main/java/io/vertx/codegen/PropertyInfo.java
@@ -108,6 +108,11 @@ public List<AnnotationValueInfo> getAnnotations() {
     return new ArrayList<>(annotations.values());
   }
 
+  /**
+   * @param annotationName fully qualified name of an annotation type
+   * @return {@link AnnotationValueInfo} for an annotation of given type present on this property,
+   * or {@code null} if an annotation of given type is not present on this property
+   */
   public AnnotationValueInfo getAnnotation(String annotationName) {
     return annotations.get(annotationName);
   }
diff --git a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/DataObjectTest.java b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/DataObjectTest.java
index 765a667bd..ec1795829 100644
--- a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/DataObjectTest.java
+++ b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/DataObjectTest.java
@@ -4,6 +4,8 @@
 import io.vertx.codegen.GenException;
 import io.vertx.codegen.PropertyInfo;
 import io.vertx.codegen.PropertyKind;
+import io.vertx.codegen.annotations.DataObject;
+import io.vertx.codegen.annotations.VertxGen;
 import io.vertx.codegen.doc.Doc;
 import io.vertx.codegen.type.*;
 import io.vertx.core.json.JsonArray;
@@ -672,7 +674,11 @@ public void testToJson() throws Exception {
   public void testAnnotatedObject() throws Exception {
     DataObjectModel model = new GeneratorHelper().generateDataObject(AnnotatedDataObject.class);
     assertEquals(2, model.getAnnotations().size());
-    assertEquals(EmptyAnnotation.class.getSimpleName(),model.getAnnotations().get(1).getSimpleName());
+    assertEquals(DataObject.class.getSimpleName(), model.getAnnotations().get(0).getSimpleName());
+    assertEquals(EmptyAnnotation.class.getSimpleName(), model.getAnnotations().get(1).getSimpleName());
+    assertTrue(model.getAnnotation(DataObject.class).isPresent());
+    assertTrue(model.getAnnotation(EmptyAnnotation.class).isPresent());
+    assertFalse(model.getAnnotation(Deprecated.class).isPresent());
   }
 
   @Test
@@ -893,9 +899,12 @@ public void testDataObjectWithAnnotations() throws Exception {
     PropertyInfo idModel = model.getPropertyMap().get("id");
     assertEquals(1, idModel.getAnnotations().size());
     assertNotNull(idModel.getAnnotation(SomeAnnotation.class.getName()).getName());
+    assertEquals(SomeAnnotation.class.getName(), idModel.getAnnotation(SomeAnnotation.class.getName()).getName());
+    assertEquals(2, idModel.getAnnotation(SomeAnnotation.class.getName()).getMember("value"));
     PropertyInfo fieldWithMethodAnnotationModel = model.getPropertyMap().get("fieldWithMethodAnnotation");
     assertEquals(2, fieldWithMethodAnnotationModel.getAnnotations().size());
     assertNotNull(fieldWithMethodAnnotationModel.getAnnotation(SomeAnnotation.class.getName()).getName());
+    assertEquals(3, fieldWithMethodAnnotationModel.getAnnotation(SomeAnnotation.class.getName()).getMember("value"));
     assertNotNull(fieldWithMethodAnnotationModel.getAnnotation(SomeMethodAnnotation.class.getName()).getName());
   }
 
diff --git a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/EnumTest.java b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/EnumTest.java
index 553dab6c8..ed398a52e 100644
--- a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/EnumTest.java
+++ b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/EnumTest.java
@@ -9,6 +9,7 @@
 import io.vertx.test.codegen.testapi.jsonmapper.WithMyCustomEnumWithMapper;
 import io.vertx.test.codegen.testenum.EnumAsParam;
 import io.vertx.test.codegen.testenum.InvalidEmptyEnum;
+import io.vertx.test.codegen.testenum.SomeAnnotation;
 import io.vertx.test.codegen.testenum.ValidEnum;
 import org.junit.Test;
 
@@ -31,6 +32,9 @@ public void testEnum() throws Exception {
     assertEquals(Arrays.asList("RED doc", "GREEN doc", "BLUE doc"), model.getValues().stream().
         map(e -> e.getDoc().toString()).
         collect(Collectors.toList()));
+    assertEquals(Arrays.asList("red", "green", "blue"), model.getValues().stream()
+      .map(e -> e.getAnnotation(SomeAnnotation.class.getName()).getMember("value"))
+      .collect(Collectors.toList()));
     assertEquals("enum", model.getKind());
     assertEquals("ValidEnum doc", model.getDoc().toString());
     assertEquals(ValidEnum.class.getName(), model.getFqn());
diff --git a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/DataObjectWithAnnotatedField.java b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/DataObjectWithAnnotatedField.java
index fe1fdfa93..2853d8269 100644
--- a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/DataObjectWithAnnotatedField.java
+++ b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/DataObjectWithAnnotatedField.java
@@ -3,18 +3,18 @@
 import io.vertx.codegen.annotations.DataObject;
 import io.vertx.core.json.JsonObject;
 
-@SomeAnnotation
+@SomeAnnotation(1)
 @DataObject(generateConverter = true)
 public class DataObjectWithAnnotatedField {
 
-  @SomeAnnotation
+  @SomeAnnotation(2)
   private Long id;
 
   private String name;
 
   private String author;
 
-  @SomeAnnotation
+  @SomeAnnotation(3)
   private String fieldWithMethodAnnotation;
 
   // Mandatory for JPA entities
diff --git a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/SomeAnnotation.java b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/SomeAnnotation.java
index 579b9eed8..e7d9930dd 100644
--- a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/SomeAnnotation.java
+++ b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testdataobject/SomeAnnotation.java
@@ -8,4 +8,5 @@
  */
 @Target({ElementType.CONSTRUCTOR, ElementType.FIELD, ElementType.TYPE})
 public @interface SomeAnnotation {
+  int value();
 }
diff --git a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/SomeAnnotation.java b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/SomeAnnotation.java
new file mode 100644
index 000000000..bfeb9da95
--- /dev/null
+++ b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/SomeAnnotation.java
@@ -0,0 +1,5 @@
+package io.vertx.test.codegen.testenum;
+
+public @interface SomeAnnotation {
+  String value();
+}
diff --git a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/ValidEnum.java b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/ValidEnum.java
index be1f97059..fa3108e75 100644
--- a/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/ValidEnum.java
+++ b/vertx-codegen-processor/src/test/java/io/vertx/test/codegen/testenum/ValidEnum.java
@@ -7,12 +7,15 @@
 public enum ValidEnum {
 
   /**RED doc*/
+  @SomeAnnotation("red")
   RED,
 
   /**GREEN doc*/
+  @SomeAnnotation("green")
   GREEN,
 
   /**BLUE doc*/
+  @SomeAnnotation("blue")
   BLUE
 
 }
diff --git a/vertx-codegen-protobuf/src/converters/generated/dataobjects.proto b/vertx-codegen-protobuf/src/converters/generated/dataobjects.proto
index 2bddf194c..b210ad988 100644
--- a/vertx-codegen-protobuf/src/converters/generated/dataobjects.proto
+++ b/vertx-codegen-protobuf/src/converters/generated/dataobjects.proto
@@ -16,12 +16,26 @@ message Address {
   float latitude = 3;
 }
 
+message Book {
+  reserved 2;
+  reserved "title";
+  string name = 1;
+  string author = 3;
+  string isbn = 10;
+  string genre = 20;
+}
+
 enum EnumType {
   A = 0;
   B = 1;
   C = 2;
 }
 
+message Person {
+  string name = 2;
+  int32 age = 4;
+}
+
 message RecursiveItem {
   string id = 1;
   RecursiveItem childA = 2;
diff --git a/vertx-codegen-protobuf/src/converters/generated/io/vertx/test/codegen/converter/BookProtoConverter.java b/vertx-codegen-protobuf/src/converters/generated/io/vertx/test/codegen/converter/BookProtoConverter.java
new file mode 100644
index 000000000..0b617d0c9
--- /dev/null
+++ b/vertx-codegen-protobuf/src/converters/generated/io/vertx/test/codegen/converter/BookProtoConverter.java
@@ -0,0 +1,91 @@
+package io.vertx.test.codegen.converter;
+
+import com.google.protobuf.CodedOutputStream;
+import com.google.protobuf.CodedInputStream;
+import java.io.IOException;
+import java.time.Instant;
+import java.time.ZonedDateTime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Arrays;
+import io.vertx.core.json.JsonObject;
+import io.vertx.codegen.protobuf.utils.ExpandableIntArray;
+import io.vertx.codegen.protobuf.converters.*;
+
+public class BookProtoConverter {
+
+  public static void fromProto(CodedInputStream input, Book obj) throws IOException {
+    int tag;
+    while ((tag = input.readTag()) != 0) {
+      switch (tag) {
+        case 10: {
+          obj.setName(input.readString());
+          break;
+        }
+        case 26: {
+          obj.setAuthor(input.readString());
+          break;
+        }
+        case 82: {
+          obj.setIsbn(input.readString());
+          break;
+        }
+        case 162: {
+          obj.setGenre(input.readString());
+          break;
+        }
+      }
+    }
+  }
+
+  public static void toProto(Book obj, CodedOutputStream output) throws IOException {
+    ExpandableIntArray cache = new ExpandableIntArray(16);
+    BookProtoConverter.computeSize(obj, cache, 0);
+    BookProtoConverter.toProto(obj, output, cache, 0);
+  }
+
+  public static int toProto(Book obj, CodedOutputStream output, ExpandableIntArray cache, int index) throws IOException {
+    index = index + 1;
+    if (obj.getName() != null) {
+      output.writeString(1, obj.getName());
+    }
+    if (obj.getAuthor() != null) {
+      output.writeString(3, obj.getAuthor());
+    }
+    if (obj.getIsbn() != null) {
+      output.writeString(10, obj.getIsbn());
+    }
+    if (obj.getGenre() != null) {
+      output.writeString(20, obj.getGenre());
+    }
+    return index;
+  }
+
+  public static int computeSize(Book obj) {
+    ExpandableIntArray cache = new ExpandableIntArray(16);
+    BookProtoConverter.computeSize(obj, cache, 0);
+    return cache.get(0);
+  }
+
+  public static int computeSize(Book obj, ExpandableIntArray cache, final int baseIndex) {
+    int size = 0;
+    int index = baseIndex + 1;
+    if (obj.getName() != null) {
+      size += CodedOutputStream.computeStringSize(1, obj.getName());
+    }
+    if (obj.getAuthor() != null) {
+      size += CodedOutputStream.computeStringSize(3, obj.getAuthor());
+    }
+    if (obj.getIsbn() != null) {
+      size += CodedOutputStream.computeStringSize(10, obj.getIsbn());
+    }
+    if (obj.getGenre() != null) {
+      size += CodedOutputStream.computeStringSize(20, obj.getGenre());
+    }
+    cache.set(baseIndex, size);
+    return index;
+  }
+
+}
diff --git a/vertx-codegen-protobuf/src/converters/generated/io/vertx/test/codegen/converter/PersonProtoConverter.java b/vertx-codegen-protobuf/src/converters/generated/io/vertx/test/codegen/converter/PersonProtoConverter.java
new file mode 100644
index 000000000..46002f198
--- /dev/null
+++ b/vertx-codegen-protobuf/src/converters/generated/io/vertx/test/codegen/converter/PersonProtoConverter.java
@@ -0,0 +1,71 @@
+package io.vertx.test.codegen.converter;
+
+import com.google.protobuf.CodedOutputStream;
+import com.google.protobuf.CodedInputStream;
+import java.io.IOException;
+import java.time.Instant;
+import java.time.ZonedDateTime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Arrays;
+import io.vertx.core.json.JsonObject;
+import io.vertx.codegen.protobuf.utils.ExpandableIntArray;
+import io.vertx.codegen.protobuf.converters.*;
+
+public class PersonProtoConverter {
+
+  public static void fromProto(CodedInputStream input, Person obj) throws IOException {
+    int tag;
+    while ((tag = input.readTag()) != 0) {
+      switch (tag) {
+        case 18: {
+          obj.setName(input.readString());
+          break;
+        }
+        case 32: {
+          obj.setAge(input.readInt32());
+          break;
+        }
+      }
+    }
+  }
+
+  public static void toProto(Person obj, CodedOutputStream output) throws IOException {
+    ExpandableIntArray cache = new ExpandableIntArray(16);
+    PersonProtoConverter.computeSize(obj, cache, 0);
+    PersonProtoConverter.toProto(obj, output, cache, 0);
+  }
+
+  public static int toProto(Person obj, CodedOutputStream output, ExpandableIntArray cache, int index) throws IOException {
+    index = index + 1;
+    if (obj.getName() != null) {
+      output.writeString(2, obj.getName());
+    }
+    if (obj.getAge() != 0) {
+      output.writeInt32(4, obj.getAge());
+    }
+    return index;
+  }
+
+  public static int computeSize(Person obj) {
+    ExpandableIntArray cache = new ExpandableIntArray(16);
+    PersonProtoConverter.computeSize(obj, cache, 0);
+    return cache.get(0);
+  }
+
+  public static int computeSize(Person obj, ExpandableIntArray cache, final int baseIndex) {
+    int size = 0;
+    int index = baseIndex + 1;
+    if (obj.getName() != null) {
+      size += CodedOutputStream.computeStringSize(2, obj.getName());
+    }
+    if (obj.getAge() != 0) {
+      size += CodedOutputStream.computeInt32Size(4, obj.getAge());
+    }
+    cache.set(baseIndex, size);
+    return index;
+  }
+
+}
diff --git a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Address.java b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Address.java
index 602df7b72..c67a2a2f9 100644
--- a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Address.java
+++ b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Address.java
@@ -1,12 +1,13 @@
 package io.vertx.test.codegen.converter;
 
 import io.vertx.codegen.annotations.DataObject;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
 import io.vertx.codegen.protobuf.annotations.ProtobufGen;
 
 import java.util.Objects;
 
 @DataObject
-@ProtobufGen
+@ProtobufGen(fieldNumberStrategy = FieldNumberStrategy.COMPACT)
 public class Address {
   private String name;
   private Float longitude;
diff --git a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Book.java b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Book.java
new file mode 100644
index 000000000..1303500d7
--- /dev/null
+++ b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Book.java
@@ -0,0 +1,64 @@
+package io.vertx.test.codegen.converter;
+
+import io.vertx.codegen.annotations.DataObject;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
+import io.vertx.codegen.protobuf.annotations.ProtobufField;
+import io.vertx.codegen.protobuf.annotations.ProtobufGen;
+
+import java.util.Objects;
+
+@DataObject
+@ProtobufGen(fieldNumberStrategy = FieldNumberStrategy.SEGMENTED, reservedFieldNumbers = 2, reservedFieldNames = "title")
+public class Book {
+  private String name;
+  private String author;
+  @ProtobufField(10)
+  private String isbn;
+  @ProtobufField(20)
+  private String genre;
+
+  public String getName() {
+    return name;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
+
+  public String getAuthor() {
+    return author;
+  }
+
+  public void setAuthor(String author) {
+    this.author = author;
+  }
+
+  public String getIsbn() {
+    return isbn;
+  }
+
+  public void setIsbn(String isbn) {
+    this.isbn = isbn;
+  }
+
+  public String getGenre() {
+    return genre;
+  }
+
+  public void setGenre(String genre) {
+    this.genre = genre;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+    Book book = (Book) o;
+    return Objects.equals(name, book.name) && Objects.equals(author, book.author) && Objects.equals(isbn, book.isbn) && Objects.equals(genre, book.genre);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(name, author, isbn, genre);
+  }
+}
diff --git a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/EnumType.java b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/EnumType.java
index 5eb6863eb..871bd052b 100644
--- a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/EnumType.java
+++ b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/EnumType.java
@@ -1,10 +1,11 @@
 package io.vertx.test.codegen.converter;
 
 import io.vertx.codegen.annotations.VertxGen;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
 import io.vertx.codegen.protobuf.annotations.ProtobufGen;
 
 @VertxGen
-@ProtobufGen
+@ProtobufGen(fieldNumberStrategy = FieldNumberStrategy.COMPACT)
 public enum EnumType {
   A,
   B,
diff --git a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Person.java b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Person.java
new file mode 100644
index 000000000..4ad8e260b
--- /dev/null
+++ b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/Person.java
@@ -0,0 +1,46 @@
+package io.vertx.test.codegen.converter;
+
+import io.vertx.codegen.annotations.DataObject;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
+import io.vertx.codegen.protobuf.annotations.ProtobufField;
+import io.vertx.codegen.protobuf.annotations.ProtobufGen;
+
+import java.util.Objects;
+
+@DataObject
+@ProtobufGen(fieldNumberStrategy = FieldNumberStrategy.MANUAL)
+public class Person {
+  @ProtobufField(2)
+  private String name;
+  @ProtobufField(4)
+  private int age;
+
+  public String getName() {
+    return name;
+  }
+
+  public void setName(String name) {
+    this.name = name;
+  }
+
+  public int getAge() {
+    return age;
+  }
+
+  public void setAge(int age) {
+    this.age = age;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+    Person person = (Person) o;
+    return Objects.equals(name, person.name) && Objects.equals(age, person.age);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(name, age);
+  }
+}
diff --git a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/RecursiveItem.java b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/RecursiveItem.java
index dd1ac5197..6c7484beb 100644
--- a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/RecursiveItem.java
+++ b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/RecursiveItem.java
@@ -1,12 +1,13 @@
 package io.vertx.test.codegen.converter;
 
 import io.vertx.codegen.annotations.DataObject;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
 import io.vertx.codegen.protobuf.annotations.ProtobufGen;
 
 import java.util.Objects;
 
 @DataObject
-@ProtobufGen
+@ProtobufGen(fieldNumberStrategy = FieldNumberStrategy.COMPACT)
 public class RecursiveItem {
 
   private String id;
diff --git a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/User.java b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/User.java
index 6efbcf7a8..421572091 100644
--- a/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/User.java
+++ b/vertx-codegen-protobuf/src/converters/java/io/vertx/test/codegen/converter/User.java
@@ -1,6 +1,7 @@
 package io.vertx.test.codegen.converter;
 
 import io.vertx.codegen.annotations.DataObject;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
 import io.vertx.codegen.protobuf.annotations.ProtobufGen;
 import io.vertx.core.json.JsonArray;
 import io.vertx.core.json.JsonObject;
@@ -12,7 +13,7 @@
 import java.util.Objects;
 
 @DataObject
-@ProtobufGen
+@ProtobufGen(fieldNumberStrategy = FieldNumberStrategy.COMPACT)
 public class User {
   private String userName;
   private Integer age;
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/FieldNumberStrategy.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/FieldNumberStrategy.java
new file mode 100644
index 000000000..ff9319475
--- /dev/null
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/FieldNumberStrategy.java
@@ -0,0 +1,45 @@
+package io.vertx.codegen.protobuf.annotations;
+
+public enum FieldNumberStrategy {
+  /**
+   * Field numbers must be assigned explicitly (using {@link ProtobufField @ProtobufField})
+   * for all properties of the data object. It is an error when two properties are assigned
+   * the same field number.
+   * <p>
+   * When removing properties, it is recommended to put their field numbers and names into
+   * the <em>reserved</em> set to prevent accidentally assigning the same field number
+   * to a different property in the future.
+   */
+  MANUAL,
+  /**
+   * Field numbers are assigned automatically for all properties of the data object.
+   * First, all properties of the data object that have an explicitly assigned field number
+   * (using {@link ProtobufField @ProtobufField}) are collected and their field numbers
+   * are remembered. Then, properties of the data object are iterated in declaration order
+   * and for each of them that does not have an explicitly assigned field number, a field
+   * number is assigned, starting from {@code 1} for the first property and increasing
+   * sequentially, skipping the explicitly assigned field numbers.
+   * <p>
+   * With this strategy, it is crucial to <strong>never remove properties</strong> (they must
+   * be either left in place or added to the <em>reserved</em> set), and <strong>always add
+   * properties at the end</strong>, even if they logically belong elsewhere.
+   */
+  COMPACT,
+  /**
+   * Field numbers are assigned automatically for all properties of the data object.
+   * The properties, taken in declaration order, are divided into segments where each
+   * property with an explicitly assigned field number (using {@link ProtobufField @ProtobufField})
+   * starts a new segment. The explicitly assigned field number that starts a segment
+   * is called the <em>initial field number</em> of the segment. There may be an additional
+   * segment at the very beginning, if the first property does not have an explicitly
+   * assigned field number; its initial field number is {@code 1}. Field numbers are
+   * assigned sequentially in each segment, where the first property of the segment
+   * has the initial field number of the segment. It is an error if two segments
+   * have overlapping field numbers.
+   * <p>
+   * With this strategy, it is crucial to <strong>never remove properties</strong> (they must
+   * be either left in place or added to the <em>reserved</em> set), and <strong>always add
+   * properties at the end of the segments</strong>, even if they logically belong elsewhere.
+   */
+  SEGMENTED,
+}
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufField.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufField.java
new file mode 100644
index 000000000..ac90443ba
--- /dev/null
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufField.java
@@ -0,0 +1,16 @@
+package io.vertx.codegen.protobuf.annotations;
+
+/**
+ * Specifies a protobuf <em>field number</em> of a property in a data class that uses {@link ProtobufGen}.
+ * See {@link ProtobufGen#fieldNumberStrategy()} for more information about how field numbers
+ * may be assigned.
+ * <p>
+ * Note that field numbers should <strong>never</strong> be changed or reused.
+ * See the <a href="https://protobuf.dev/programming-guides/proto3/">Protocol Buffers Language Guide</a>
+ * for more information.
+ * <p>
+ * Currently, this annotation is ignored on enum values. That may change in the future.
+ */
+public @interface ProtobufField {
+  int value();
+}
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufGen.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufGen.java
index a98b6b829..0e785e52b 100644
--- a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufGen.java
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/annotations/ProtobufGen.java
@@ -32,4 +32,31 @@
  */
 public @interface ProtobufGen {
   JsonProtoEncoding jsonProtoEncoding() default JsonProtoEncoding.VERTX_STRUCT;
+
+  /**
+   * The strategy of field number assignment. Use {@link FieldNumberStrategy#MANUAL},
+   * {@link FieldNumberStrategy#COMPACT}, or {@link FieldNumberStrategy#SEGMENTED}.
+   * <p>
+   * See the <a href="https://protobuf.dev/programming-guides/proto3/">Protocol Buffers Language Guide</a>
+   * for more information about protobuf schema evolution.
+   * <p>
+   * Note that this setting is ignored for {@code enum}s, where protobuf enum constants are always
+   * assigned automatically. Coincidentally, the protobuf enum constants are identical to
+   * {@linkplain Enum#ordinal() enum ordinals}. Extra <strong>care must be taken when changing
+   * {@code enum}s</strong> annotated {@code @ProtobufGen}. In the future, this setting may become
+   * relevant even for enums, together with {@link ProtobufField @ProtobufField}.
+   */
+  FieldNumberStrategy fieldNumberStrategy();
+
+  /**
+   * The set of reserved field numbers. It is an error for a data object property to be explicitly assigned
+   * a field number from the reserved set. Automatically assigned field numbers will skip the reserved numbers.
+   */
+  int[] reservedFieldNumbers() default {};
+
+  /**
+   * The set of reserved field names. It is an error for a data object property to have a name that is
+   * present in the reserved set.
+   */
+  String[] reservedFieldNames() default {};
 }
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/DataObjectProtobufGen.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/DataObjectProtobufGen.java
index 99bc6db30..876719f7c 100644
--- a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/DataObjectProtobufGen.java
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/DataObjectProtobufGen.java
@@ -3,6 +3,7 @@
 import io.vertx.codegen.DataObjectModel;
 import io.vertx.codegen.Generator;
 import io.vertx.codegen.PropertyInfo;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
 import io.vertx.codegen.protobuf.annotations.JsonProtoEncoding;
 import io.vertx.codegen.protobuf.annotations.ProtobufGen;
 import io.vertx.codegen.type.ClassKind;
@@ -14,7 +15,9 @@
 import java.lang.annotation.Annotation;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 /**
  * @author <a href="mailto:julien@julienviet.com">Julien Viet</a>
@@ -52,7 +55,10 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
     CodeWriter code = new CodeWriter(writer);
     String visibility = model.isPublicConverter() ? "public" : "";
 
-    JsonProtoEncoding jsonProtoEncoding = JsonProtoEncodingSelector.select(model);
+    JsonProtoEncoding jsonProtoEncoding = ProtobufGenAnnotation.jsonProtoEncoding(model);
+    FieldNumberStrategy fieldNumberStrategy = ProtobufGenAnnotation.fieldNumberStrategy(model);
+    Set<Integer> reservedFieldNumbers = ProtobufGenAnnotation.reservedFieldNumbers(model);
+    Set<String> reservedFieldNames = ProtobufGenAnnotation.reservedFieldNames(model);
 
     writer.print("package " + model.getType().getPackageName() + ";\n");
     writer.print("\n");
@@ -76,15 +82,20 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
 
     String simpleName = model.getType().getSimpleName();
 
+    Collection<PropertyInfo> properties = model.getPropertyMap().values();
+    ProtobufFields.verifyFieldNames(properties, reservedFieldNames);
+    Map<String, Integer> fieldNumbers = ProtobufFields.fieldNumbers(properties, fieldNumberStrategy, reservedFieldNumbers);
+    List<PropertyInfo> orderedProperties = ProtobufFields.inFieldNumberOrder(properties, fieldNumbers);
+
     // fromProto()
     {
       writer.print("  " + visibility + " static void fromProto(CodedInputStream input, " + simpleName + " obj) throws IOException {\n");
       writer.print("    int tag;\n");
       writer.print("    while ((tag = input.readTag()) != 0) {\n");
       writer.print("      switch (tag) {\n");
-      int fieldNumber = 1;
-      for (PropertyInfo prop : model.getPropertyMap().values()) {
+      for (PropertyInfo prop : orderedProperties) {
         ClassKind propKind = prop.getType().getKind();
+        int fieldNumber = fieldNumbers.get(prop.getName());
         ProtoProperty protoProperty = ProtoProperty.getProtoProperty(prop, fieldNumber);
         writer.print("        case " + protoProperty.getTag() + ": {\n");
         if (prop.getType().getKind() == ClassKind.ENUM) {
@@ -223,7 +234,6 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
           }
         } // Not Enum
         writer.print("        }\n");
-        fieldNumber++;
       }
       writer.print("      }\n");
       writer.print("    }\n");
@@ -241,9 +251,9 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
       writer.print("\n");
       writer.print("  " + visibility + " static int toProto(" + simpleName + " obj, CodedOutputStream output, ExpandableIntArray cache, int index) throws IOException {\n");
       writer.print("    index = index + 1;\n");
-      int fieldNumber = 1;
-      for (PropertyInfo prop : model.getPropertyMap().values()) {
+      for (PropertyInfo prop : orderedProperties) {
         ClassKind propKind = prop.getType().getKind();
+        int fieldNumber = fieldNumbers.get(prop.getName());
         ProtoProperty protoProperty = ProtoProperty.getProtoProperty(prop, fieldNumber);
         if (protoProperty.isNullable()) {
           writer.print("    if (obj." + prop.getGetterMethod() + "() != null) {\n");
@@ -375,7 +385,6 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
           }
         } // Not Enum
         writer.print("    }\n");
-        fieldNumber++;
       }
       writer.print("    return index;\n");
       writer.print("  }\n");
@@ -393,9 +402,9 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
       writer.print("  " + visibility + " static int computeSize(" + simpleName + " obj, ExpandableIntArray cache, final int baseIndex) {\n");
       writer.print("    int size = 0;\n");
       writer.print("    int index = baseIndex + 1;\n");
-      int fieldNumber = 1;
-      for (PropertyInfo prop : model.getPropertyMap().values()) {
+      for (PropertyInfo prop : orderedProperties) {
         ClassKind propKind = prop.getType().getKind();
+        int fieldNumber = fieldNumbers.get(prop.getName());
         ProtoProperty protoProperty = ProtoProperty.getProtoProperty(prop, fieldNumber);
         if (protoProperty.isNullable()) {
           writer.print("    if (obj." + prop.getGetterMethod() + "() != null) {\n");
@@ -530,7 +539,6 @@ public String renderProto(DataObjectModel model, int index, int size, Map<String
           }
         } // Not Enum
         writer.print("    }\n");
-        fieldNumber++;
       }
       writer.print("    cache.set(baseIndex, size);\n");
       writer.print("    return index;\n");
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/JsonProtoEncodingSelector.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/JsonProtoEncodingSelector.java
deleted file mode 100644
index c9345b5cf..000000000
--- a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/JsonProtoEncodingSelector.java
+++ /dev/null
@@ -1,22 +0,0 @@
-package io.vertx.codegen.protobuf.generator;
-
-import io.vertx.codegen.DataObjectModel;
-import io.vertx.codegen.protobuf.annotations.JsonProtoEncoding;
-import io.vertx.codegen.protobuf.annotations.ProtobufGen;
-
-import java.util.Optional;
-
-// Extract JsonProtoEncoding from Annotation attribute ProtobufGen.jsonProtoEncoding()
-public class JsonProtoEncodingSelector {
-  static public JsonProtoEncoding select(DataObjectModel model) {
-    Optional<Object> opMember = model.getAnnotations()
-      .stream()
-      .filter(ann -> ann.getName().equals(ProtobufGen.class.getName()))
-      .findFirst()
-      .map(ann -> ann.getMember("jsonProtoEncoding"));
-
-    return opMember
-      .map(v -> JsonProtoEncoding.valueOf((String) v))
-      .orElse(JsonProtoEncoding.VERTX_STRUCT); // Default to VERTX_STRUCT
-  }
-}
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoFileGen.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoFileGen.java
index b0c309da1..5205aaba2 100644
--- a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoFileGen.java
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoFileGen.java
@@ -1,9 +1,7 @@
 package io.vertx.codegen.protobuf.generator;
 
 import io.vertx.codegen.*;
-import io.vertx.codegen.annotations.DataObject;
-import io.vertx.codegen.annotations.ModuleGen;
-import io.vertx.codegen.annotations.VertxGen;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
 import io.vertx.codegen.protobuf.annotations.JsonProtoEncoding;
 import io.vertx.codegen.protobuf.annotations.ProtobufGen;
 import io.vertx.codegen.type.ClassKind;
@@ -14,7 +12,10 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 public class ProtoFileGen extends Generator<Model> {
 
@@ -69,7 +70,10 @@ private String renderDataObjectModel(DataObjectModel model, int index) {
     StringWriter buffer = new StringWriter();
     PrintWriter writer = new PrintWriter(buffer);
 
-    JsonProtoEncoding jsonProtoEncoding = JsonProtoEncodingSelector.select(model);
+    JsonProtoEncoding jsonProtoEncoding = ProtobufGenAnnotation.jsonProtoEncoding(model);
+    FieldNumberStrategy fieldNumberStrategy = ProtobufGenAnnotation.fieldNumberStrategy(model);
+    Set<Integer> reservedFieldNumbers = ProtobufGenAnnotation.reservedFieldNumbers(model);
+    Set<String> reservedFieldNames = ProtobufGenAnnotation.reservedFieldNames(model);
 
     if (index == 0) {
       writer.print("// Automatically generated by vertx-codegen.\n");
@@ -91,11 +95,34 @@ private String renderDataObjectModel(DataObjectModel model, int index) {
     }
 
     String messageName = model.getType().getSimpleName();
-    int fieldNumber = 1;
+
+    Collection<PropertyInfo> properties = model.getPropertyMap().values();
+    ProtobufFields.verifyFieldNames(properties, reservedFieldNames);
+    Map<String, Integer> fieldNumbers = ProtobufFields.fieldNumbers(properties, fieldNumberStrategy, reservedFieldNumbers);
+    List<PropertyInfo> orderedProperties = ProtobufFields.inFieldNumberOrder(properties, fieldNumbers);
 
     writer.print("message " + messageName + " {\n");
-    for (PropertyInfo prop : model.getPropertyMap().values()) {
+
+    if (!reservedFieldNumbers.isEmpty()) {
+      writer.print("  reserved ");
+      writer.print(reservedFieldNumbers.stream()
+        .sorted()
+        .map(it -> "" + it)
+        .collect(Collectors.joining(", ")));
+      writer.print(";\n");
+    }
+    if (!reservedFieldNames.isEmpty()) {
+      writer.print("  reserved ");
+      writer.print(reservedFieldNames.stream()
+        .sorted()
+        .map(it -> '"' + it + '"')
+        .collect(Collectors.joining(", ")));
+      writer.print(";\n");
+    }
+
+    for (PropertyInfo prop : orderedProperties) {
       ClassKind propKind = prop.getType().getKind();
+      int fieldNumber = fieldNumbers.get(prop.getName());
       ProtoProperty protoProperty = ProtoProperty.getProtoProperty(prop, fieldNumber);
 
       String protoFieldType;
@@ -120,7 +147,6 @@ private String renderDataObjectModel(DataObjectModel model, int index) {
       } else {
         writer.print("  " + protoFieldType + " " + prop.getName() + " = " + fieldNumber + ";\n");
       }
-      fieldNumber++;
     }
     writer.print("}\n");
     writer.print("\n");
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoProperty.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoProperty.java
index 505c83d59..f8a2f17ae 100644
--- a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoProperty.java
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtoProperty.java
@@ -68,6 +68,8 @@ public static ProtoProperty getProtoProperty(PropertyInfo prop, int fieldNumber)
       wireType = 2;
     }
 
+    checkFieldNumber(fieldNumber);
+
     int tag = (fieldNumber << 3) | wireType;
 
     protoProperty.fieldNumber = fieldNumber;
@@ -81,6 +83,16 @@ public static ProtoProperty getProtoProperty(PropertyInfo prop, int fieldNumber)
     return protoProperty;
   }
 
+  private static void checkFieldNumber(int fieldNumber) {
+    // see https://protobuf.dev/programming-guides/proto3/#assigning
+    if (fieldNumber < 1 || fieldNumber > 536_870_911) {
+      throw new IllegalArgumentException("Field number " + fieldNumber + " is invalid");
+    }
+    if (fieldNumber >= 19_000 && fieldNumber <= 19_999) {
+      throw new IllegalArgumentException("Field number " + fieldNumber + " is reserved for Protobuf implementations");
+    }
+  }
+
   private static ProtoType determinePrimitiveProtoType(String javaDataType) {
     if ("java.lang.Integer".equals(javaDataType) || "int".equals(javaDataType)) {
       return ProtoType.INT32;
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtobufFields.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtobufFields.java
new file mode 100644
index 000000000..7de463978
--- /dev/null
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtobufFields.java
@@ -0,0 +1,149 @@
+package io.vertx.codegen.protobuf.generator;
+
+import io.vertx.codegen.PropertyInfo;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
+import io.vertx.codegen.protobuf.annotations.ProtobufField;
+import io.vertx.codegen.type.AnnotationValueInfo;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+class ProtobufFields {
+  private static final String PROTOBUF_FIELD_ANNOTATION_NAME = ProtobufField.class.getName();
+
+  static void verifyFieldNames(Collection<PropertyInfo> props, Set<String> reservedFieldNames) {
+    for (PropertyInfo prop : props) {
+      if (reservedFieldNames.contains(prop.getName())) {
+        throw new IllegalArgumentException("Field name '" + prop.getName() + "' is reserved");
+      }
+    }
+  }
+
+  static Map<String, Integer> fieldNumbers(Collection<PropertyInfo> props, FieldNumberStrategy fieldNumberStrategy,
+      Set<Integer> reservedFieldNumbers) {
+    switch (fieldNumberStrategy) {
+      case MANUAL:
+        return manualFieldNumbers(props, reservedFieldNumbers);
+      case COMPACT:
+        return compactFieldNumbers(props, reservedFieldNumbers);
+      case SEGMENTED:
+        return segmentedFieldNumbers(props, reservedFieldNumbers);
+      default:
+        throw new IllegalArgumentException("Unknown field number strategy: " + fieldNumberStrategy);
+    }
+  }
+
+  private static Map<String, Integer> manualFieldNumbers(Collection<PropertyInfo> props, Set<Integer> reservedFieldNumbers) {
+    Map<String, Integer> result = new HashMap<>();
+    Map<Integer, String> alreadyUsed = new HashMap<>();
+    for (PropertyInfo prop : props) {
+      AnnotationValueInfo ann = prop.getAnnotation(PROTOBUF_FIELD_ANNOTATION_NAME);
+      if (ann != null) {
+        Integer fieldNumber = (Integer) ann.getMember("value");
+        if (reservedFieldNumbers.contains(fieldNumber)) {
+          throw new IllegalArgumentException("Property '" + prop.getName()
+            + "' has a reserved field number " + fieldNumber);
+        }
+        if (alreadyUsed.containsKey(fieldNumber)) {
+          String collidingProperty = alreadyUsed.get(fieldNumber);
+          throw new IllegalArgumentException("Property '" + prop.getName() + "' is assigned field number "
+            + fieldNumber + ", which collides with property '" + collidingProperty + "'");
+        }
+        result.put(prop.getName(), fieldNumber);
+        alreadyUsed.put(fieldNumber, prop.getName());
+      } else {
+        throw new IllegalArgumentException("Property '" + prop.getName()
+          + "' does not declare a field number; use @ProtobufField");
+      }
+    }
+    return result;
+  }
+
+  private static Map<String, Integer> compactFieldNumbers(Collection<PropertyInfo> props, Set<Integer> reservedFieldNumbers) {
+    Map<String, Integer> result = new HashMap<>();
+    Map<Integer, String> alreadyUsed = new HashMap<>();
+    // 1. find pre-allocated field numbers
+    for (PropertyInfo prop : props) {
+      AnnotationValueInfo ann = prop.getAnnotation(PROTOBUF_FIELD_ANNOTATION_NAME);
+      if (ann != null) {
+        Integer fieldNumber = (Integer) ann.getMember("value");
+        if (reservedFieldNumbers.contains(fieldNumber)) {
+          throw new IllegalArgumentException("Property '" + prop.getName()
+            + "' has a reserved field number " + fieldNumber);
+        }
+        if (alreadyUsed.containsKey(fieldNumber)) {
+          String collidingProperty = alreadyUsed.get(fieldNumber);
+          throw new IllegalArgumentException("Property '" + prop.getName() + "' is assigned field number "
+            + fieldNumber + ", which collides with property '" + collidingProperty + "'");
+        }
+        result.put(prop.getName(), fieldNumber);
+        alreadyUsed.put(fieldNumber, prop.getName());
+      }
+    }
+    // 2. allocate field numbers to properties that don't have one pre-allocated
+    int lastFieldNumber = 1;
+    for (PropertyInfo prop : props) {
+      if (result.containsKey(prop.getName())) {
+        continue;
+      }
+      while (alreadyUsed.containsKey(lastFieldNumber) || reservedFieldNumbers.contains(lastFieldNumber)) {
+        lastFieldNumber++;
+      }
+      result.put(prop.getName(), lastFieldNumber++);
+    }
+    return result;
+  }
+
+  private static Map<String, Integer> segmentedFieldNumbers(Collection<PropertyInfo> props, Set<Integer> reservedFieldNumbers) {
+    Map<String, Integer> result = new HashMap<>();
+    Map<Integer, String> alreadyUsed = new HashMap<>();
+    int lastFieldNumber = 0;
+    for (PropertyInfo prop : props) {
+      AnnotationValueInfo ann = prop.getAnnotation(PROTOBUF_FIELD_ANNOTATION_NAME);
+      if (ann != null) {
+        lastFieldNumber = (Integer) ann.getMember("value");
+        if (reservedFieldNumbers.contains(lastFieldNumber)) {
+          throw new IllegalArgumentException("Property '" + prop.getName()
+            + "' has a reserved field number " + lastFieldNumber);
+        }
+      } else {
+        lastFieldNumber++;
+        while (reservedFieldNumbers.contains(lastFieldNumber)) {
+          lastFieldNumber++;
+        }
+      }
+      if (alreadyUsed.containsKey(lastFieldNumber)) {
+        String collidingProperty = alreadyUsed.get(lastFieldNumber);
+        throw new IllegalArgumentException("Property '" + prop.getName() + "' is assigned field number "
+          + lastFieldNumber + ", which collides with property '" + collidingProperty + "'");
+      }
+      result.put(prop.getName(), lastFieldNumber);
+      alreadyUsed.put(lastFieldNumber, prop.getName());
+    }
+    return result;
+  }
+
+  /**
+   * Returns a list with the same elements as the given collection of properties, except
+   * the list is ordered so that properties with lower protobuf field number precede
+   * properties with higher protobuf field number.
+   *
+   * @param props a collection of {@link PropertyInfo}s
+   * @param fieldNumbers field numbers for all properties
+   * @return a list of the same {@link PropertyInfo}s, in field number order
+   */
+  static List<PropertyInfo> inFieldNumberOrder(Collection<PropertyInfo> props, Map<String, Integer> fieldNumbers) {
+    List<PropertyInfo> result = new ArrayList<>(props);
+    result.sort((a, b) -> {
+      Integer ai = fieldNumbers.get(a.getName());
+      Integer bi = fieldNumbers.get(b.getName());
+      // there should be no `null` values at the moment
+      return Integer.compare(ai != null ? ai : 0, bi != null ? bi : 0);
+    });
+    return result;
+  }
+}
diff --git a/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtobufGenAnnotation.java b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtobufGenAnnotation.java
new file mode 100644
index 000000000..43eeb4e3a
--- /dev/null
+++ b/vertx-codegen-protobuf/src/main/java/io/vertx/codegen/protobuf/generator/ProtobufGenAnnotation.java
@@ -0,0 +1,44 @@
+package io.vertx.codegen.protobuf.generator;
+
+import io.vertx.codegen.DataObjectModel;
+import io.vertx.codegen.Model;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
+import io.vertx.codegen.protobuf.annotations.JsonProtoEncoding;
+import io.vertx.codegen.protobuf.annotations.ProtobufGen;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.Set;
+
+class ProtobufGenAnnotation {
+  static JsonProtoEncoding jsonProtoEncoding(DataObjectModel model) {
+    return model.getAnnotation(ProtobufGen.class)
+      .map(ann -> ann.getMember("jsonProtoEncoding"))
+      .map(v -> JsonProtoEncoding.valueOf((String) v))
+      .orElse(JsonProtoEncoding.VERTX_STRUCT); // Default to VERTX_STRUCT
+  }
+
+  static FieldNumberStrategy fieldNumberStrategy(Model model) {
+    return model.getAnnotation(ProtobufGen.class)
+      .map(ann -> (String) ann.getMember("fieldNumberStrategy"))
+      .map(FieldNumberStrategy::valueOf)
+      .orElseThrow(NoSuchElementException::new); // the annotation member is mandatory, so this should never happen
+  }
+
+  static Set<Integer> reservedFieldNumbers(Model model) {
+    return model.getAnnotation(ProtobufGen.class)
+      .map(ann -> (List<Integer>) ann.getMember("reservedFieldNumbers"))
+      .map(HashSet::new)
+      .orElseGet(HashSet::new);
+  }
+
+  static Set<String> reservedFieldNames(Model model) {
+    return model.getAnnotation(ProtobufGen.class)
+      .map(ann -> (List<String>) ann.getMember("reservedFieldNames"))
+      .map(HashSet::new)
+      .orElseGet(HashSet::new);
+  }
+}
diff --git a/vertx-codegen-protobuf/src/test/java/io/vertx/codegen/protobuf/generator/ProtobufFieldsTest.java b/vertx-codegen-protobuf/src/test/java/io/vertx/codegen/protobuf/generator/ProtobufFieldsTest.java
new file mode 100644
index 000000000..5a74e3b43
--- /dev/null
+++ b/vertx-codegen-protobuf/src/test/java/io/vertx/codegen/protobuf/generator/ProtobufFieldsTest.java
@@ -0,0 +1,179 @@
+package io.vertx.codegen.protobuf.generator;
+
+import io.vertx.codegen.PropertyInfo;
+import io.vertx.codegen.PropertyKind;
+import io.vertx.codegen.protobuf.annotations.FieldNumberStrategy;
+import io.vertx.codegen.protobuf.annotations.ProtobufField;
+import io.vertx.codegen.type.AnnotationValueInfo;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+
+public class ProtobufFieldsTest {
+  private static PropertyInfo prop(String name, Integer fieldNumberAnnotation) {
+    List<AnnotationValueInfo> anns = new ArrayList<>();
+    if (fieldNumberAnnotation != null) {
+      AnnotationValueInfo ann = new AnnotationValueInfo(ProtobufField.class.getName());
+      ann.putMember("value", fieldNumberAnnotation);
+      anns.add(ann);
+    }
+    return new PropertyInfo(true, name, null, null, null, null, null,
+      anns, PropertyKind.VALUE, true, false, null);
+  }
+
+  @Test
+  public void verifyFieldNames() {
+    List<PropertyInfo> props = Arrays.asList(
+      prop("foo", null),
+      prop("bar", null));
+
+    // doesn't throw
+    ProtobufFields.verifyFieldNames(props, Collections.singleton("baz"));
+
+    IllegalArgumentException error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.verifyFieldNames(props, Collections.singleton("foo"));
+    });
+    assertTrue(error.getMessage().contains("is reserved"));
+
+    assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.verifyFieldNames(props, new HashSet<>(Arrays.asList("foo", "bar")));
+    });
+    assertTrue(error.getMessage().contains("is reserved"));
+
+    assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.verifyFieldNames(props, new HashSet<>(Arrays.asList("foo", "baz")));
+    });
+    assertTrue(error.getMessage().contains("is reserved"));
+  }
+
+  @Test
+  public void manualFieldNumbers() {
+    IllegalArgumentException error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(prop("foo", null)),
+        FieldNumberStrategy.MANUAL, Collections.emptySet());
+    });
+    assertTrue(error.getMessage().contains("does not declare a field number"));
+
+    error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(Arrays.asList(
+          prop("foo", 1),
+          prop("bar", 1)),
+        FieldNumberStrategy.MANUAL, Collections.emptySet());
+    });
+    assertTrue(error.getMessage().contains("collides with property"));
+
+    error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(prop("foo", 1)),
+        FieldNumberStrategy.MANUAL, Collections.singleton(1));
+    });
+    assertTrue(error.getMessage().contains("has a reserved field number"));
+
+    Map<String, Integer> fieldNumbers = ProtobufFields.fieldNumbers(
+      Arrays.asList(
+        prop("foo", 1),
+        prop("bar", 5),
+        prop("baz", 7),
+        prop("quux", 3)),
+      FieldNumberStrategy.MANUAL, Collections.emptySet());
+    assertEquals(1, (int) fieldNumbers.get("foo"));
+    assertEquals(5, (int) fieldNumbers.get("bar"));
+    assertEquals(7, (int) fieldNumbers.get("baz"));
+    assertEquals(3, (int) fieldNumbers.get("quux"));
+  }
+
+  @Test
+  public void compactFieldNumbers() {
+    IllegalArgumentException error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(prop("foo", 1)),
+        FieldNumberStrategy.COMPACT, Collections.singleton(1));
+    });
+    assertTrue(error.getMessage().contains("has a reserved field number"));
+
+    error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(
+          prop("foo", 1),
+          prop("bar", 1)),
+        FieldNumberStrategy.COMPACT, Collections.emptySet());
+    });
+    assertTrue(error.getMessage().contains("collides with property"));
+
+    Map<String, Integer> fieldNumbers = ProtobufFields.fieldNumbers(
+      Arrays.asList(
+        prop("foo", 1),
+        prop("bar", null),
+        prop("baz", 3),
+        prop("quux", null)),
+      FieldNumberStrategy.COMPACT, Collections.singleton(2));
+    assertEquals(1, (int) fieldNumbers.get("foo"));
+    assertEquals(4, (int) fieldNumbers.get("bar"));
+    assertEquals(3, (int) fieldNumbers.get("baz"));
+    assertEquals(5, (int) fieldNumbers.get("quux"));
+  }
+
+  @Test
+  public void segmentedFieldNumbers() {
+    IllegalArgumentException error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(prop("foo", 1)),
+        FieldNumberStrategy.SEGMENTED, Collections.singleton(1));
+    });
+    assertTrue(error.getMessage().contains("has a reserved field number"));
+
+    error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(
+          prop("foo", 1),
+          prop("bar", 1)),
+        FieldNumberStrategy.SEGMENTED, Collections.emptySet());
+    });
+    assertTrue(error.getMessage().contains("collides with property"));
+
+    error = assertThrows(IllegalArgumentException.class, () -> {
+      ProtobufFields.fieldNumbers(
+        Arrays.asList(
+          prop("foo", null),
+          prop("bar", null),
+          prop("baz", null),
+          prop("quux", 3)),
+        FieldNumberStrategy.SEGMENTED, Collections.emptySet());
+    });
+    assertTrue(error.getMessage().contains("collides with property"));
+
+    Map<String, Integer> fieldNumbers = ProtobufFields.fieldNumbers(
+      Arrays.asList(
+        prop("foo", null),
+        prop("bar", 5),
+        prop("baz", 10),
+        prop("quux", null)),
+      FieldNumberStrategy.SEGMENTED, Collections.singleton(2));
+    assertEquals(1, (int) fieldNumbers.get("foo"));
+    assertEquals(5, (int) fieldNumbers.get("bar"));
+    assertEquals(10, (int) fieldNumbers.get("baz"));
+    assertEquals(11, (int) fieldNumbers.get("quux"));
+
+    fieldNumbers = ProtobufFields.fieldNumbers(
+      Arrays.asList(
+        prop("foo", null),
+        prop("bar", null),
+        prop("baz", 3),
+        prop("quux", null)),
+      FieldNumberStrategy.SEGMENTED, Collections.singleton(4));
+    assertEquals(1, (int) fieldNumbers.get("foo"));
+    assertEquals(2, (int) fieldNumbers.get("bar"));
+    assertEquals(3, (int) fieldNumbers.get("baz"));
+    assertEquals(5, (int) fieldNumbers.get("quux"));
+  }
+}