diff --git a/csharp/src/Google.Protobuf.Test/JsonParserTest.cs b/csharp/src/Google.Protobuf.Test/JsonParserTest.cs
new file mode 100644
index 0000000..d21da58
--- /dev/null
+++ b/csharp/src/Google.Protobuf.Test/JsonParserTest.cs
@@ -0,0 +1,925 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using Google.Protobuf.Reflection;
+using Google.Protobuf.TestProtos;
+using Google.Protobuf.WellKnownTypes;
+using NUnit.Framework;
+using System;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Unit tests for JSON parsing.
+    /// </summary>
+    public class JsonParserTest
+    {
+        // Sanity smoke test
+        [Test]
+        public void AllTypesRoundtrip()
+        {
+            AssertRoundtrip(SampleMessages.CreateFullTestAllTypes());
+        }
+
+        [Test]
+        public void Maps()
+        {
+            AssertRoundtrip(new TestMap { MapStringString = { { "with spaces", "bar" }, { "a", "b" } } });
+            AssertRoundtrip(new TestMap { MapInt32Int32 = { { 0, 1 }, { 2, 3 } } });
+            AssertRoundtrip(new TestMap { MapBoolBool = { { false, true }, { true, false } } });
+        }
+
+        [Test]
+        [TestCase(" 1 ")]
+        [TestCase("+1")]
+        [TestCase("1,000")]
+        [TestCase("1.5")]
+        public void IntegerMapKeysAreStrict(string keyText)
+        {
+            // Test that integer parsing is strict. We assume that if this is correct for int32,
+            // it's correct for other numeric key types.
+            var json = "{ \"mapInt32Int32\": { \"" + keyText + "\" : \"1\" } }";
+            Assert.Throws<InvalidProtocolBufferException>(() => JsonParser.Default.Parse<TestMap>(json));
+        }
+
+        [Test]
+        public void OriginalFieldNameAccepted()
+        {
+            var json = "{ \"single_int32\": 10 }";
+            var expected = new TestAllTypes { SingleInt32 = 10 };
+            Assert.AreEqual(expected, TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void SourceContextRoundtrip()
+        {
+            AssertRoundtrip(new SourceContext { FileName = "foo.proto" });
+        }
+
+        [Test]
+        public void SingularWrappers_DefaultNonNullValues()
+        {
+            var message = new TestWellKnownTypes
+            {
+                StringField = "",
+                BytesField = ByteString.Empty,
+                BoolField = false,
+                FloatField = 0f,
+                DoubleField = 0d,
+                Int32Field = 0,
+                Int64Field = 0,
+                Uint32Field = 0,
+                Uint64Field = 0
+            };
+            AssertRoundtrip(message);
+        }
+
+        [Test]
+        public void SingularWrappers_NonDefaultValues()
+        {
+            var message = new TestWellKnownTypes
+            {
+                StringField = "x",
+                BytesField = ByteString.CopyFrom(1, 2, 3),
+                BoolField = true,
+                FloatField = 12.5f,
+                DoubleField = 12.25d,
+                Int32Field = 1,
+                Int64Field = 2,
+                Uint32Field = 3,
+                Uint64Field = 4
+            };
+            AssertRoundtrip(message);
+        }
+
+        [Test]
+        public void SingularWrappers_ExplicitNulls()
+        {
+            // When we parse the "valueField": null part, we remember it... basically, it's one case
+            // where explicit default values don't fully roundtrip.
+            var message = new TestWellKnownTypes { ValueField = Value.ForNull() };
+            var json = new JsonFormatter(new JsonFormatter.Settings(true)).Format(message);
+            var parsed = JsonParser.Default.Parse<TestWellKnownTypes>(json);
+            Assert.AreEqual(message, parsed);
+        }
+
+        [Test]
+        [TestCase(typeof(Int32Value), "32", 32)]
+        [TestCase(typeof(Int64Value), "32", 32L)]
+        [TestCase(typeof(UInt32Value), "32", 32U)]
+        [TestCase(typeof(UInt64Value), "32", 32UL)]
+        [TestCase(typeof(StringValue), "\"foo\"", "foo")]
+        [TestCase(typeof(FloatValue), "1.5", 1.5f)]
+        [TestCase(typeof(DoubleValue), "1.5", 1.5d)]
+        public void Wrappers_Standalone(System.Type wrapperType, string json, object expectedValue)
+        {
+            IMessage parsed = (IMessage) Activator.CreateInstance(wrapperType);
+            IMessage expected = (IMessage) Activator.CreateInstance(wrapperType);
+            JsonParser.Default.Merge(parsed, "null");
+            Assert.AreEqual(expected, parsed);
+
+            JsonParser.Default.Merge(parsed, json);
+            expected.Descriptor.Fields[WrappersReflection.WrapperValueFieldNumber].Accessor.SetValue(expected, expectedValue);
+            Assert.AreEqual(expected, parsed);
+        }
+
+        [Test]
+        public void ExplicitNullValue()
+        {
+            string json = "{\"valueField\": null}";
+            var message = JsonParser.Default.Parse<TestWellKnownTypes>(json);
+            Assert.AreEqual(new TestWellKnownTypes { ValueField = Value.ForNull() }, message);
+        }
+
+        [Test]
+        public void BytesWrapper_Standalone()
+        {
+            ByteString data = ByteString.CopyFrom(1, 2, 3);
+            // Can't do this with attributes...
+            var parsed = JsonParser.Default.Parse<BytesValue>(WrapInQuotes(data.ToBase64()));
+            var expected = new BytesValue { Value = data };
+            Assert.AreEqual(expected, parsed);
+        }
+
+        [Test]
+        public void RepeatedWrappers()
+        {
+            var message = new RepeatedWellKnownTypes
+            {
+                BoolField = { true, false },
+                BytesField = { ByteString.CopyFrom(1, 2, 3), ByteString.CopyFrom(4, 5, 6), ByteString.Empty },
+                DoubleField = { 12.5, -1.5, 0d },
+                FloatField = { 123.25f, -20f, 0f },
+                Int32Field = { int.MaxValue, int.MinValue, 0 },
+                Int64Field = { long.MaxValue, long.MinValue, 0L },
+                StringField = { "First", "Second", "" },
+                Uint32Field = { uint.MaxValue, uint.MinValue, 0U },
+                Uint64Field = { ulong.MaxValue, ulong.MinValue, 0UL },
+            };
+            AssertRoundtrip(message);
+        }
+
+        [Test]
+        public void RepeatedField_NullElementProhibited()
+        {
+            string json = "{ \"repeated_foreign_message\": [null] }";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void RepeatedField_NullOverallValueAllowed()
+        {
+            string json = "{ \"repeated_foreign_message\": null }";
+            Assert.AreEqual(new TestAllTypes(), TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("{ \"mapInt32Int32\": { \"10\": null }")]
+        [TestCase("{ \"mapStringString\": { \"abc\": null }")]
+        [TestCase("{ \"mapInt32ForeignMessage\": { \"10\": null }")]
+        public void MapField_NullValueProhibited(string json)
+        {
+            Assert.Throws<InvalidProtocolBufferException>(() => TestMap.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void MapField_NullOverallValueAllowed()
+        {
+            string json = "{ \"mapInt32Int32\": null }";
+            Assert.AreEqual(new TestMap(), TestMap.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void IndividualWrapperTypes()
+        {
+            Assert.AreEqual(new StringValue { Value = "foo" }, StringValue.Parser.ParseJson("\"foo\""));
+            Assert.AreEqual(new Int32Value { Value = 1 }, Int32Value.Parser.ParseJson("1"));
+            // Can parse strings directly too
+            Assert.AreEqual(new Int32Value { Value = 1 }, Int32Value.Parser.ParseJson("\"1\""));
+        }
+
+        private static void AssertRoundtrip<T>(T message) where T : IMessage<T>, new()
+        {
+            var clone = message.Clone();
+            var json = JsonFormatter.Default.Format(message);
+            var parsed = JsonParser.Default.Parse<T>(json);
+            Assert.AreEqual(clone, parsed);
+        }
+
+        [Test]
+        [TestCase("0", 0)]
+        [TestCase("-0", 0)] // Not entirely clear whether we intend to allow this...
+        [TestCase("1", 1)]
+        [TestCase("-1", -1)]
+        [TestCase("2147483647", 2147483647)]
+        [TestCase("-2147483648", -2147483648)]
+        public void StringToInt32_Valid(string jsonValue, int expectedParsedValue)
+        {
+            string json = "{ \"singleInt32\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt32);
+        }
+
+        [Test]
+        [TestCase("+0")]
+        [TestCase(" 1")]
+        [TestCase("1 ")]
+        [TestCase("00")]
+        [TestCase("-00")]
+        [TestCase("--1")]
+        [TestCase("+1")]
+        [TestCase("1.5")]
+        [TestCase("1e10")]
+        [TestCase("2147483648")]
+        [TestCase("-2147483649")]
+        public void StringToInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt32\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0U)]
+        [TestCase("1", 1U)]
+        [TestCase("4294967295", 4294967295U)]
+        public void StringToUInt32_Valid(string jsonValue, uint expectedParsedValue)
+        {
+            string json = "{ \"singleUint32\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint32);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("4294967296")]
+        public void StringToUInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint32\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0L)]
+        [TestCase("1", 1L)]
+        [TestCase("-1", -1L)]
+        [TestCase("9223372036854775807", 9223372036854775807)]
+        [TestCase("-9223372036854775808", -9223372036854775808)]
+        public void StringToInt64_Valid(string jsonValue, long expectedParsedValue)
+        {
+            string json = "{ \"singleInt64\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-9223372036854775809")]
+        [TestCase("9223372036854775808")]
+        public void StringToInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt64\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0UL)]
+        [TestCase("1", 1UL)]
+        [TestCase("18446744073709551615", 18446744073709551615)]
+        public void StringToUInt64_Valid(string jsonValue, ulong expectedParsedValue)
+        {
+            string json = "{ \"singleUint64\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("18446744073709551616")]
+        public void StringToUInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint64\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0d)]
+        [TestCase("1", 1d)]
+        [TestCase("1.000000", 1d)]
+        [TestCase("1.0000000000000000000000001", 1d)] // We don't notice that we haven't preserved the exact value
+        [TestCase("-1", -1d)]
+        [TestCase("1e1", 10d)]
+        [TestCase("1e01", 10d)] // Leading decimals are allowed in exponents
+        [TestCase("1E1", 10d)] // Either case is fine
+        [TestCase("-1e1", -10d)]
+        [TestCase("1.5e1", 15d)]
+        [TestCase("-1.5e1", -15d)]
+        [TestCase("15e-1", 1.5d)]
+        [TestCase("-15e-1", -1.5d)]
+        [TestCase("1.79769e308", 1.79769e308)]
+        [TestCase("-1.79769e308", -1.79769e308)]
+        [TestCase("Infinity", double.PositiveInfinity)]
+        [TestCase("-Infinity", double.NegativeInfinity)]
+        [TestCase("NaN", double.NaN)]
+        public void StringToDouble_Valid(string jsonValue, double expectedParsedValue)
+        {
+            string json = "{ \"singleDouble\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleDouble);
+        }
+
+        [Test]
+        [TestCase("1.7977e308")]
+        [TestCase("-1.7977e308")]
+        [TestCase("1e309")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("01")]
+        [TestCase("-00")]
+        [TestCase("-01")]
+        [TestCase("--1")]
+        [TestCase(" Infinity")]
+        [TestCase(" -Infinity")]
+        [TestCase("NaN ")]
+        [TestCase("Infinity ")]
+        [TestCase("-Infinity ")]
+        [TestCase(" NaN")]
+        [TestCase("INFINITY")]
+        [TestCase("nan")]
+        [TestCase("\u00BD")] // 1/2 as a single Unicode character. Just sanity checking...
+        public void StringToDouble_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleDouble\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0f)]
+        [TestCase("1", 1f)]
+        [TestCase("1.000000", 1f)]
+        [TestCase("-1", -1f)]
+        [TestCase("3.402823e38", 3.402823e38f)]
+        [TestCase("-3.402823e38", -3.402823e38f)]
+        [TestCase("1.5e1", 15f)]
+        [TestCase("15e-1", 1.5f)]
+        public void StringToFloat_Valid(string jsonValue, float expectedParsedValue)
+        {
+            string json = "{ \"singleFloat\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleFloat);
+        }
+
+        [Test]
+        [TestCase("3.402824e38")]
+        [TestCase("-3.402824e38")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("--1")]
+        public void StringToFloat_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleFloat\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0)]
+        [TestCase("-0", 0)] // Not entirely clear whether we intend to allow this...
+        [TestCase("1", 1)]
+        [TestCase("-1", -1)]
+        [TestCase("2147483647", 2147483647)]
+        [TestCase("-2147483648", -2147483648)]
+        [TestCase("1e1", 10)]
+        [TestCase("-1e1", -10)]
+        [TestCase("10.00", 10)]
+        [TestCase("-10.00", -10)]
+        public void NumberToInt32_Valid(string jsonValue, int expectedParsedValue)
+        {
+            string json = "{ \"singleInt32\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt32);
+        }
+
+        [Test]
+        [TestCase("+0", typeof(InvalidJsonException))]
+        [TestCase("00", typeof(InvalidJsonException))]
+        [TestCase("-00", typeof(InvalidJsonException))]
+        [TestCase("--1", typeof(InvalidJsonException))]
+        [TestCase("+1", typeof(InvalidJsonException))]
+        [TestCase("1.5", typeof(InvalidProtocolBufferException))]
+        // Value is out of range
+        [TestCase("1e10", typeof(InvalidProtocolBufferException))]
+        [TestCase("2147483648", typeof(InvalidProtocolBufferException))]
+        [TestCase("-2147483649", typeof(InvalidProtocolBufferException))]
+        public void NumberToInt32_Invalid(string jsonValue, System.Type expectedExceptionType)
+        {
+            string json = "{ \"singleInt32\": " + jsonValue + "}";
+            Assert.Throws(expectedExceptionType, () => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0U)]
+        [TestCase("1", 1U)]
+        [TestCase("4294967295", 4294967295U)]
+        public void NumberToUInt32_Valid(string jsonValue, uint expectedParsedValue)
+        {
+            string json = "{ \"singleUint32\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint32);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("4294967296")]
+        public void NumberToUInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint32\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0L)]
+        [TestCase("1", 1L)]
+        [TestCase("-1", -1L)]
+        // long.MaxValue isn't actually representable as a double. This string value is the highest
+        // representable value which isn't greater than long.MaxValue.
+        [TestCase("9223372036854774784", 9223372036854774784)]
+        [TestCase("-9223372036854775808", -9223372036854775808)]
+        public void NumberToInt64_Valid(string jsonValue, long expectedParsedValue)
+        {
+            string json = "{ \"singleInt64\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("9223372036854775808")]
+        // Theoretical bound would be -9223372036854775809, but when that is parsed to a double
+        // we end up with the exact value of long.MinValue due to lack of precision. The value here
+        // is the "next double down".
+        [TestCase("-9223372036854780000")]
+        public void NumberToInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt64\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0UL)]
+        [TestCase("1", 1UL)]
+        // ulong.MaxValue isn't representable as a double. This value is the largest double within
+        // the range of ulong.
+        [TestCase("18446744073709549568", 18446744073709549568UL)]
+        public void NumberToUInt64_Valid(string jsonValue, ulong expectedParsedValue)
+        {
+            string json = "{ \"singleUint64\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("18446744073709551616")]
+        public void NumberToUInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint64\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0d)]
+        [TestCase("1", 1d)]
+        [TestCase("1.000000", 1d)]
+        [TestCase("1.0000000000000000000000001", 1d)] // We don't notice that we haven't preserved the exact value
+        [TestCase("-1", -1d)]
+        [TestCase("1e1", 10d)]
+        [TestCase("1e01", 10d)] // Leading decimals are allowed in exponents
+        [TestCase("1E1", 10d)] // Either case is fine
+        [TestCase("-1e1", -10d)]
+        [TestCase("1.5e1", 15d)]
+        [TestCase("-1.5e1", -15d)]
+        [TestCase("15e-1", 1.5d)]
+        [TestCase("-15e-1", -1.5d)]
+        [TestCase("1.79769e308", 1.79769e308)]
+        [TestCase("-1.79769e308", -1.79769e308)]
+        public void NumberToDouble_Valid(string jsonValue, double expectedParsedValue)
+        {
+            string json = "{ \"singleDouble\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleDouble);
+        }
+
+        [Test]
+        [TestCase("1.7977e308")]
+        [TestCase("-1.7977e308")]
+        [TestCase("1e309")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("--1")]
+        [TestCase("\u00BD")] // 1/2 as a single Unicode character. Just sanity checking...
+        public void NumberToDouble_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleDouble\": " + jsonValue + "}";
+            Assert.Throws<InvalidJsonException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0f)]
+        [TestCase("1", 1f)]
+        [TestCase("1.000000", 1f)]
+        [TestCase("-1", -1f)]
+        [TestCase("3.402823e38", 3.402823e38f)]
+        [TestCase("-3.402823e38", -3.402823e38f)]
+        [TestCase("1.5e1", 15f)]
+        [TestCase("15e-1", 1.5f)]
+        public void NumberToFloat_Valid(string jsonValue, float expectedParsedValue)
+        {
+            string json = "{ \"singleFloat\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleFloat);
+        }
+
+        [Test]
+        [TestCase("3.402824e38", typeof(InvalidProtocolBufferException))]
+        [TestCase("-3.402824e38", typeof(InvalidProtocolBufferException))]
+        [TestCase("1,0", typeof(InvalidJsonException))]
+        [TestCase("1.0.0", typeof(InvalidJsonException))]
+        [TestCase("+1", typeof(InvalidJsonException))]
+        [TestCase("00", typeof(InvalidJsonException))]
+        [TestCase("--1", typeof(InvalidJsonException))]
+        public void NumberToFloat_Invalid(string jsonValue, System.Type expectedExceptionType)
+        {
+            string json = "{ \"singleFloat\": " + jsonValue + "}";
+            Assert.Throws(expectedExceptionType, () => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        // The simplest way of testing that the value has parsed correctly is to reformat it,
+        // as we trust the formatting. In many cases that will give the same result as the input,
+        // so in those cases we accept an expectedFormatted value of null. Sometimes the results
+        // will be different though, due to a different number of digits being provided.
+        [Test]
+        // Z offset
+        [TestCase("2015-10-09T14:46:23.123456789Z", null)]
+        [TestCase("2015-10-09T14:46:23.123456Z", null)]
+        [TestCase("2015-10-09T14:46:23.123Z", null)]
+        [TestCase("2015-10-09T14:46:23Z", null)]
+        [TestCase("2015-10-09T14:46:23.123456000Z", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.1234560Z", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.123000000Z", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.1230Z", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.00Z", "2015-10-09T14:46:23Z")]
+
+        // +00:00 offset
+        [TestCase("2015-10-09T14:46:23.123456789+00:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T14:46:23.123456+00:00", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.123+00:00", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23+00:00", "2015-10-09T14:46:23Z")]
+        [TestCase("2015-10-09T14:46:23.123456000+00:00", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.1234560+00:00", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.123000000+00:00", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.1230+00:00", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.00+00:00", "2015-10-09T14:46:23Z")]
+
+        // Other offsets (assume by now that the subsecond handling is okay)
+        [TestCase("2015-10-09T15:46:23.123456789+01:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T13:46:23.123456789-01:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T15:16:23.123456789+00:30", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T14:16:23.123456789-00:30", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T16:31:23.123456789+01:45", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T13:01:23.123456789-01:45", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-10T08:46:23.123456789+18:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-08T20:46:23.123456789-18:00", "2015-10-09T14:46:23.123456789Z")]
+
+        // Leap years and min/max
+        [TestCase("2016-02-29T14:46:23.123456789Z", null)]
+        [TestCase("2000-02-29T14:46:23.123456789Z", null)]
+        [TestCase("0001-01-01T00:00:00Z", null)]
+        [TestCase("9999-12-31T23:59:59.999999999Z", null)]
+        public void Timestamp_Valid(string jsonValue, string expectedFormatted)
+        {
+            expectedFormatted = expectedFormatted ?? jsonValue;
+            string json = WrapInQuotes(jsonValue);
+            var parsed = Timestamp.Parser.ParseJson(json);
+            Assert.AreEqual(WrapInQuotes(expectedFormatted), parsed.ToString());
+        }
+        
+        [Test]
+        [TestCase("2015-10-09 14:46:23.123456789Z", Description = "No T between date and time")]
+        [TestCase("2015/10/09T14:46:23.123456789Z", Description = "Wrong date separators")]
+        [TestCase("2015-10-09T14.46.23.123456789Z", Description = "Wrong time separators")]
+        [TestCase("2015-10-09T14:46:23,123456789Z", Description = "Wrong fractional second separators (valid ISO-8601 though)")]
+        [TestCase(" 2015-10-09T14:46:23.123456789Z", Description = "Whitespace at start")]
+        [TestCase("2015-10-09T14:46:23.123456789Z ", Description = "Whitespace at end")]
+        [TestCase("2015-10-09T14:46:23.1234567890", Description = "Too many digits")]
+        [TestCase("2015-10-09T14:46:23.123456789", Description = "No offset")]
+        [TestCase("2015-13-09T14:46:23.123456789Z", Description = "Invalid month")]
+        [TestCase("2015-10-32T14:46:23.123456789Z", Description = "Invalid day")]
+        [TestCase("2015-10-09T24:00:00.000000000Z", Description = "Invalid hour (valid ISO-8601 though)")]
+        [TestCase("2015-10-09T14:60:23.123456789Z", Description = "Invalid minutes")]
+        [TestCase("2015-10-09T14:46:60.123456789Z", Description = "Invalid seconds")]
+        [TestCase("2015-10-09T14:46:23.123456789+18:01", Description = "Offset too large (positive)")]
+        [TestCase("2015-10-09T14:46:23.123456789-18:01", Description = "Offset too large (negative)")]
+        [TestCase("2015-10-09T14:46:23.123456789-00:00", Description = "Local offset (-00:00) makes no sense here")]
+        [TestCase("0001-01-01T00:00:00+00:01", Description = "Value before earliest when offset applied")]
+        [TestCase("9999-12-31T23:59:59.999999999-00:01", Description = "Value after latest when offset applied")]
+        [TestCase("2100-02-29T14:46:23.123456789Z", Description = "Feb 29th on a non-leap-year")]
+        public void Timestamp_Invalid(string jsonValue)
+        {
+            string json = WrapInQuotes(jsonValue);
+            Assert.Throws<InvalidProtocolBufferException>(() => Timestamp.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void StructValue_Null()
+        {
+            Assert.AreEqual(new Value { NullValue = 0 }, Value.Parser.ParseJson("null"));
+        }
+
+        [Test]
+        public void StructValue_String()
+        {
+            Assert.AreEqual(new Value { StringValue = "hi" }, Value.Parser.ParseJson("\"hi\""));
+        }
+
+        [Test]
+        public void StructValue_Bool()
+        {
+            Assert.AreEqual(new Value { BoolValue = true }, Value.Parser.ParseJson("true"));
+            Assert.AreEqual(new Value { BoolValue = false }, Value.Parser.ParseJson("false"));
+        }
+
+        [Test]
+        public void StructValue_List()
+        {
+            Assert.AreEqual(Value.ForList(Value.ForNumber(1), Value.ForString("x")), Value.Parser.ParseJson("[1, \"x\"]"));
+        }
+
+        [Test]
+        public void ParseListValue()
+        {
+            Assert.AreEqual(new ListValue { Values = { Value.ForNumber(1), Value.ForString("x") } }, ListValue.Parser.ParseJson("[1, \"x\"]"));
+        }
+
+        [Test]
+        public void StructValue_Struct()
+        {
+            Assert.AreEqual(
+                Value.ForStruct(new Struct { Fields = { { "x", Value.ForNumber(1) }, { "y", Value.ForString("z") } } }),
+                Value.Parser.ParseJson("{ \"x\": 1, \"y\": \"z\" }"));
+        }
+
+        [Test]
+        public void ParseStruct()
+        {
+            Assert.AreEqual(new Struct { Fields = { { "x", Value.ForNumber(1) }, { "y", Value.ForString("z") } } },
+                Struct.Parser.ParseJson("{ \"x\": 1, \"y\": \"z\" }"));
+        }
+
+        // TODO for duration parsing: upper and lower bounds.
+        // +/- 315576000000 seconds
+
+        [Test]
+        [TestCase("1.123456789s", null)]
+        [TestCase("1.123456s", null)]
+        [TestCase("1.123s", null)]
+        [TestCase("1.12300s", "1.123s")]
+        [TestCase("1.12345s", "1.123450s")]
+        [TestCase("1s", null)]
+        [TestCase("-1.123456789s", null)]
+        [TestCase("-1.123456s", null)]
+        [TestCase("-1.123s", null)]
+        [TestCase("-1s", null)]
+        [TestCase("0.123s", null)]
+        [TestCase("-0.123s", null)]
+        [TestCase("123456.123s", null)]
+        [TestCase("-123456.123s", null)]
+        // Upper and lower bounds
+        [TestCase("315576000000s", null)]
+        [TestCase("-315576000000s", null)]
+        public void Duration_Valid(string jsonValue, string expectedFormatted)
+        {
+            expectedFormatted = expectedFormatted ?? jsonValue;
+            string json = WrapInQuotes(jsonValue);
+            var parsed = Duration.Parser.ParseJson(json);
+            Assert.AreEqual(WrapInQuotes(expectedFormatted), parsed.ToString());
+        }
+
+        // The simplest way of testing that the value has parsed correctly is to reformat it,
+        // as we trust the formatting. In many cases that will give the same result as the input,
+        // so in those cases we accept an expectedFormatted value of null. Sometimes the results
+        // will be different though, due to a different number of digits being provided.
+        [Test]
+        [TestCase("1.1234567890s", Description = "Too many digits")]
+        [TestCase("1.123456789", Description = "No suffix")]
+        [TestCase("1.123456789ss", Description = "Too much suffix")]
+        [TestCase("1.123456789S", Description = "Upper case suffix")]
+        [TestCase("+1.123456789s", Description = "Leading +")]
+        [TestCase(".123456789s", Description = "No integer before the fraction")]
+        [TestCase("1,123456789s", Description = "Comma as decimal separator")]
+        [TestCase("1x1.123456789s", Description = "Non-digit in integer part")]
+        [TestCase("1.1x3456789s", Description = "Non-digit in fractional part")]
+        [TestCase(" 1.123456789s", Description = "Whitespace before fraction")]
+        [TestCase("1.123456789s ", Description = "Whitespace after value")]
+        [TestCase("01.123456789s", Description = "Leading zero (positive)")]
+        [TestCase("-01.123456789s", Description = "Leading zero (negative)")]
+        [TestCase("--0.123456789s", Description = "Double minus sign")]
+        // Violate upper/lower bounds in various ways
+        [TestCase("315576000001s", Description = "Integer part too large")]
+        [TestCase("3155760000000s", Description = "Integer part too long (positive)")]
+        [TestCase("-3155760000000s", Description = "Integer part too long (negative)")]
+        public void Duration_Invalid(string jsonValue)
+        {
+            string json = WrapInQuotes(jsonValue);
+            Assert.Throws<InvalidProtocolBufferException>(() => Duration.Parser.ParseJson(json));
+        }
+
+        // Not as many tests for field masks as I'd like; more to be added when we have more
+        // detailed specifications.
+
+        [Test]
+        [TestCase("")]
+        [TestCase("foo", "foo")]
+        [TestCase("foo,bar", "foo", "bar")]
+        [TestCase("foo.bar", "foo.bar")]
+        [TestCase("fooBar", "foo_bar")]
+        [TestCase("fooBar.bazQux", "foo_bar.baz_qux")]
+        public void FieldMask_Valid(string jsonValue, params string[] expectedPaths)
+        {
+            string json = WrapInQuotes(jsonValue);
+            var parsed = FieldMask.Parser.ParseJson(json);
+            CollectionAssert.AreEqual(expectedPaths, parsed.Paths);
+        }
+
+        [Test]
+        [TestCase("foo_bar")]
+        public void FieldMask_Invalid(string jsonValue)
+        {
+            string json = WrapInQuotes(jsonValue);
+            Assert.Throws<InvalidProtocolBufferException>(() => FieldMask.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void Any_RegularMessage()
+        {
+            var registry = TypeRegistry.FromMessages(TestAllTypes.Descriptor);
+            var formatter = new JsonFormatter(new JsonFormatter.Settings(false, TypeRegistry.FromMessages(TestAllTypes.Descriptor)));
+            var message = new TestAllTypes { SingleInt32 = 10, SingleNestedMessage = new TestAllTypes.Types.NestedMessage { Bb = 20 } };
+            var original = Any.Pack(message);
+            var json = formatter.Format(original); // This is tested in JsonFormatterTest
+            var parser = new JsonParser(new JsonParser.Settings(10, registry));
+            Assert.AreEqual(original, parser.Parse<Any>(json));
+            string valueFirstJson = "{ \"singleInt32\": 10, \"singleNestedMessage\": { \"bb\": 20 }, \"@type\": \"type.googleapis.com/protobuf_unittest.TestAllTypes\" }";
+            Assert.AreEqual(original, parser.Parse<Any>(valueFirstJson));
+        }
+
+        [Test]
+        public void Any_UnknownType()
+        {
+            string json = "{ \"@type\": \"type.googleapis.com/bogus\" }";
+            Assert.Throws<InvalidOperationException>(() => Any.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void Any_NoTypeUrl()
+        {
+            string json = "{ \"foo\": \"bar\" }";
+            Assert.Throws<InvalidProtocolBufferException>(() => Any.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void Any_WellKnownType()
+        {
+            var registry = TypeRegistry.FromMessages(Timestamp.Descriptor);
+            var formatter = new JsonFormatter(new JsonFormatter.Settings(false, registry));
+            var timestamp = new DateTime(1673, 6, 19, 12, 34, 56, DateTimeKind.Utc).ToTimestamp();
+            var original = Any.Pack(timestamp);
+            var json = formatter.Format(original); // This is tested in JsonFormatterTest
+            var parser = new JsonParser(new JsonParser.Settings(10, registry));
+            Assert.AreEqual(original, parser.Parse<Any>(json));
+            string valueFirstJson = "{ \"value\": \"1673-06-19T12:34:56Z\", \"@type\": \"type.googleapis.com/google.protobuf.Timestamp\" }";
+            Assert.AreEqual(original, parser.Parse<Any>(valueFirstJson));
+        }
+
+        [Test]
+        public void Any_Nested()
+        {
+            var registry = TypeRegistry.FromMessages(TestWellKnownTypes.Descriptor, TestAllTypes.Descriptor);
+            var formatter = new JsonFormatter(new JsonFormatter.Settings(false, registry));
+            var parser = new JsonParser(new JsonParser.Settings(10, registry));
+            var doubleNestedMessage = new TestAllTypes { SingleInt32 = 20 };
+            var nestedMessage = Any.Pack(doubleNestedMessage);
+            var message = new TestWellKnownTypes { AnyField = Any.Pack(nestedMessage) };
+            var json = formatter.Format(message);
+            // Use the descriptor-based parser just for a change.
+            Assert.AreEqual(message, parser.Parse(json, TestWellKnownTypes.Descriptor));
+        }
+
+        [Test]
+        public void DataAfterObject()
+        {
+            string json = "{} 10";
+            Assert.Throws<InvalidJsonException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        /// <summary>
+        /// JSON equivalent to <see cref="CodedInputStreamTest.MaliciousRecursion"/>
+        /// </summary>
+        [Test]
+        public void MaliciousRecursion()
+        {
+            string data64 = CodedInputStreamTest.MakeRecursiveMessage(64).ToString();
+            string data65 = CodedInputStreamTest.MakeRecursiveMessage(65).ToString();
+
+            var parser64 = new JsonParser(new JsonParser.Settings(64));
+            CodedInputStreamTest.AssertMessageDepth(parser64.Parse<TestRecursiveMessage>(data64), 64);
+            Assert.Throws<InvalidProtocolBufferException>(() => parser64.Parse<TestRecursiveMessage>(data65));
+
+            var parser63 = new JsonParser(new JsonParser.Settings(63));
+            Assert.Throws<InvalidProtocolBufferException>(() => parser63.Parse<TestRecursiveMessage>(data64));
+        }
+
+        [Test]
+        [TestCase("AQI")]
+        [TestCase("_-==")]
+        public void Bytes_InvalidBase64(string badBase64)
+        {
+            string json = "{ \"singleBytes\": \"" + badBase64 + "\" }";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("\"FOREIGN_BAR\"", ForeignEnum.FOREIGN_BAR)]
+        [TestCase("5", ForeignEnum.FOREIGN_BAR)]
+        [TestCase("100", (ForeignEnum) 100)]
+        public void EnumValid(string value, ForeignEnum expectedValue)
+        {
+            string json = "{ \"singleForeignEnum\": " + value + " }";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(new TestAllTypes { SingleForeignEnum = expectedValue }, parsed);
+        }
+
+        [Test]
+        [TestCase("\"NOT_A_VALID_VALUE\"")]
+        [TestCase("5.5")]
+        public void Enum_Invalid(string value)
+        {
+            string json = "{ \"singleForeignEnum\": " + value + " }";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void OneofDuplicate_Invalid()
+        {
+            string json = "{ \"oneofString\": \"x\", \"oneofUint32\": 10 }";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        /// <summary>
+        /// Various tests use strings which have quotes round them for parsing or as the result
+        /// of formatting, but without those quotes being specified in the tests (for the sake of readability).
+        /// This method simply returns the input, wrapped in double quotes.
+        /// </summary>
+        internal static string WrapInQuotes(string text)
+        {
+            return '"' + text + '"';
+        }
+    }
+}