diff --git a/README.md b/README.md
index 401fe73..5849e72 100644
--- a/README.md
+++ b/README.md
@@ -75,9 +75,11 @@ Here's a more complicated example that shows more options being used:
     # release of fourmolu will be used.
     version: "0.13.0.0"
 
-    # Only check the format of .hs in the src/ directory.
+    # Only check the format of .hs in the src/ directory
+    # except src/Main.hs.
     pattern: |
       src/**/*.hs
+      !src/Main.hs
 
     # Don't follow symbolic links to .hs files.
     follow-symbolic-links: false
@@ -86,6 +88,8 @@ Here's a more complicated example that shows more options being used:
     extra-args: "--indent-wheres true"
 ```
 
+See [docs](https://github.com/actions/toolkit/tree/main/packages/glob#patterns) on pattern syntax.
+
 ### Example usage with build matrix
 
 If you are using a build matrix, then it is more efficient to have a
diff --git a/action.yml b/action.yml
index 540d545..c16d391 100644
--- a/action.yml
+++ b/action.yml
@@ -3,9 +3,19 @@ description: 'Check formatting of Haskell code with Fourmolu'
 inputs:
   pattern:
     required: false
-    description: >
-      Glob pattern that are used to find source files to format. It is
-      possible to specify several patterns by putting each on a new line.
+    description: |
+      Glob pattern that is used to find source files to format.
+
+      See [docs](https://github.com/actions/toolkit/tree/main/packages/glob#patterns) on pattern syntax.
+
+      It is possible to specify several patterns by putting each one on a new line.
+
+      ```yaml
+      src/**/*.hs
+      !src/Main.hs
+      ```
+
+      `src/Main.hs` will be skipped.
     default: |
       **/*.hs
       **/*.hs-boot