diff --git a/doc/api.rst b/doc/api.rst
index 12e420f..ad03a3b 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -173,6 +173,8 @@ Formats
 
     a default :class:`.LineFormat` for use in the shell.  Same as :data:`.line_format` but uses :data:`.shell_conversion` for :attr:`.fields`.
 
+.. autoclass:: JSONFormat
+
 *************************
 Levels
 *************************
@@ -393,12 +395,12 @@ Outputs
         Class variable, indicating that locks should be used when running in a synchronous, multithreaded environment. Threadsafe subclasses may disable locking for higher throughput. Defaults to True.
 
     .. automethod:: __init__
-    
+
     .. versionadded:: 0.4.1
-        Add the `close_atexit` parameter.     
-    
+        Add the `close_atexit` parameter.
+
     .. method:: close
-        
+
         Finalize the output.
 
     The following methods should be implemented by subclasses.
@@ -428,7 +430,7 @@ Outputs
 .. autoclass:: NullOutput
 
 .. autoclass:: ListOutput
-    
+
 .. versionchanged:: 0.4.1
     Replace `DequeOutput` with more useful `ListOutput`.
 
diff --git a/tests/test_formats.py b/tests/test_formats.py
index b3d79ee..9c3fbbe 100644
--- a/tests/test_formats.py
+++ b/tests/test_formats.py
@@ -52,7 +52,7 @@ def test_shell_conversion(self):
             formats.shell_format.conversion.convert(d)
 
 
-class FormatTestCase(unittest.TestCase):
+class LineFormatTestCase(unittest.TestCase):
 
     fields = {'time': when,
               'level': levels.INFO,
@@ -142,3 +142,48 @@ def test_trace_fold(self):
         s = fmt(msg)
         lines = s.split('\n')
         assert len(lines) == 2
+
+class JSONFormatTestCase(unittest.TestCase):
+
+    fields = {'time': when,
+              'level': levels.INFO,
+              'name': 'mylog',
+              'pants': 42,
+              }
+
+    def test_basic(self):
+
+        fmt = formats.JSONFormat()
+
+        opts = message.Message._default_options.copy()
+        msg = message.Message(levels.INFO, "I wear {0}", self.fields, opts, ['pants'], {})
+        assert fmt(msg) == '2010-10-28T02:15:57Z:INFO:mylog:pants=42|I wear pants\n'
+
+    def test_inline_fields(self):
+
+        fmt = formats.JSONFormat(inline_fields=True)
+
+        opts = message.Message._default_options.copy()
+        msg = message.Message(levels.INFO, "I wear {0}", self.fields, opts, ['pants'], {})
+        assert fmt(msg) == '2010-10-28T02:15:57Z:INFO:mylog:pants=42|I wear pants\n'
+
+
+    def test_trace(self):
+
+        fmt = formats.JSONFormat()
+
+        opts = message.Message._default_options.copy()
+        opts['trace'] = 'error'
+
+        try:
+            1 / 0
+        except ZeroDivisionError:
+            msg = message.Message(levels.INFO, "I wear {0}", self.fields, opts, ['pants'], {})
+
+        s = fmt(msg)
+        lines = s.split('\n')
+        assert len(lines) == 6
+        for i in lines[1:-1]:
+            assert i.startswith('TRACE')
+
+        assert lines[0] == '2010-10-28T02:15:57Z:INFO:mylog:pants=42|I wear pants'
diff --git a/tests/test_lib_json.py b/tests/test_lib_json.py
new file mode 100644
index 0000000..8d0f1c1
--- /dev/null
+++ b/tests/test_lib_json.py
@@ -0,0 +1,21 @@
+import datetime
+import decimal
+import json
+import re
+import unittest
+
+from twiggy.lib.json import TwiggyJSONEncoder
+
+class TwiggyJSONEncoderTests(unittest.TestCase):
+    def test_timedelta(self):
+        duration = datetime.timedelta(days=1, hours=2, seconds=3)
+        self.assertEqual(
+            json.dumps({'duration': duration}, cls=TwiggyJSONEncoder),
+            '{"duration": "P1DT02H00M03S"}'
+        )
+        duration = datetime.timedelta(0)
+        self.assertEqual(
+            json.dumps({'duration': duration}, cls=TwiggyJSONEncoder),
+            '{"duration": "P0DT00H00M00S"}'
+        )
+
diff --git a/twiggy/formats.py b/twiggy/formats.py
index 6c15d5c..a820e00 100644
--- a/twiggy/formats.py
+++ b/twiggy/formats.py
@@ -1,6 +1,8 @@
 import copy
+import json
 
 from .lib.converter import ConversionTable, Converter
+from .lib.json import TwiggyJSONEncoder
 from .lib import iso8601time
 
 #: a default line-oriented converter
@@ -72,3 +74,27 @@ def format_fields(self, msg):
 #: a format for use in the shell - no timestamp
 shell_format = copy.copy(line_format)
 shell_format.conversion.get('time').convert_item = lambda k, v: None
+
+import json
+
+class JSONFormat(object):
+    """format messages to JSON. Returns a string.
+
+    The resulting JSON will have keys: `text`, `traceback` (possibly null) and `fields`.
+    Set `inline_fields` to True to include fields directly instead.
+
+    :ivar bool inline_fields: hoist individual fields to top-level keys. Defaults to False.
+    :ivar dict kwargs: extra keyword arguments to pass to `json.dumps()`
+    """
+
+    def __init__(self, inline_fields=False, **kwargs):
+        self.inline_fields = inline_fields
+        self.kwargs = kwargs
+
+    def __call__(self, msg):
+        # XXX this ignores msg.suppress_newlines. Hmm.
+        return json.dumps(
+            {'text': msg.text,
+             'traceback': msg.traceback,
+             **(msg.fields if self.inline_fields else {'fields': msg.fields})},
+            cls=TwiggyJSONEncoder, **self.kwargs)
diff --git a/twiggy/lib/json.py b/twiggy/lib/json.py
new file mode 100644
index 0000000..fb79693
--- /dev/null
+++ b/twiggy/lib/json.py
@@ -0,0 +1,97 @@
+import datetime
+import decimal
+import json
+import time
+import uuid
+
+from ..levels import LogLevel
+
+class TwiggyJSONEncoder(json.JSONEncoder):
+    """
+    JSONEncoder subclass that knows how to encode date/time, decimal types, UUIDs and LogLevels.
+
+    Based on DjangoJSONEncoder.
+    """
+    def default(self, o):
+        if isinstance(o, LogLevel):
+            return str(o)
+        elif isinstance(o, (decimal.Decimal, uuid.UUID)):
+            return str(o)
+        elif isinstance(o, time.struct_time):
+            # XXX broken, as we never reach this function (or even encode()), since struct_time is a
+            # tuple, and JSONEncoder handles it before we get here. Hmm.
+
+            # convert struct_time to datetime
+            o = datetime.datetime.fromtimestamp(time.mktime(o))
+
+        # See "Date Time String Format" in the ECMA-262 specification.
+        if isinstance(o, datetime.datetime):
+            r = o.isoformat()
+            if o.microsecond:
+                r = r[:23] + r[26:]
+            if r.endswith('+00:00'):
+                r = r[:-6] + 'Z'
+            return r
+        elif isinstance(o, datetime.date):
+            return o.isoformat()
+        elif isinstance(o, datetime.time):
+            if is_aware(o):
+                raise ValueError("JSON can't represent timezone-aware times.")
+            r = o.isoformat()
+            if o.microsecond:
+                r = r[:12]
+            return r
+        elif isinstance(o, datetime.timedelta):
+            return duration_iso_string(o)
+        else:
+            return super().default(o)
+
+
+def _get_duration_components(duration):
+    days = duration.days
+    seconds = duration.seconds
+    microseconds = duration.microseconds
+
+    minutes = seconds // 60
+    seconds = seconds % 60
+
+    hours = minutes // 60
+    minutes = minutes % 60
+
+    return days, hours, minutes, seconds, microseconds
+
+
+def duration_string(duration):
+    """Version of str(timedelta) which is not English specific."""
+    days, hours, minutes, seconds, microseconds = _get_duration_components(duration)
+
+    string = '{:02d}:{:02d}:{:02d}'.format(hours, minutes, seconds)
+    if days:
+        string = '{} '.format(days) + string
+    if microseconds:
+        string += '.{:06d}'.format(microseconds)
+
+    return string
+
+
+def duration_iso_string(duration):
+    if duration < datetime.timedelta(0):
+        sign = '-'
+        duration *= -1
+    else:
+        sign = ''
+
+    days, hours, minutes, seconds, microseconds = _get_duration_components(duration)
+    ms = '.{:06d}'.format(microseconds) if microseconds else ""
+    return '{}P{}DT{:02d}H{:02d}M{:02d}{}S'.format(sign, days, hours, minutes, seconds, ms)
+
+
+def is_aware(value):
+    """
+    Determine if a given datetime.datetime is aware.
+    The concept is defined in Python's docs:
+    http://docs.python.org/library/datetime.html#datetime.tzinfo
+    Assuming value.tzinfo is either None or a proper datetime.tzinfo,
+    value.utcoffset() implements the appropriate logic.
+    """
+    return value.utcoffset() is not None