Accept numeric JSON-RPC ids and progress tokens

CHANGELOG.md

@@ -121,6 +121,9 @@
   tool parameter headers, including requested `Mcp-Param-*` headers.
 - Serialized MRTR `ElicitResult` and `ListRootsResult` input responses with the
   MCP 2026 embedded client-result shapes that omit common Result `_meta`.
+- Accepted finite numeric JSON-RPC request IDs and progress tokens, matching
+  the stable and MCP 2026 `string | number` schema while continuing to reject
+  non-finite numbers.
 
 ## 2.2.0
 

lib/src/shared/transport.dart

@@ -45,21 +45,22 @@ abstract class Transport {
 }
 
 /// Optional capability for transports that can preserve JSON-RPC request IDs
-/// with their full MCP shape (string or integer) for request/stream correlation.
+/// with their full MCP shape (string or finite number) for request/stream
+/// correlation.
 ///
 /// Existing custom transports can keep implementing [Transport.send] with
 /// `int? relatedRequestId`. Transports that need to route messages by string
 /// request IDs should also implement this interface.
 abstract class RequestIdAwareTransport {
-  /// Sends a JSON-RPC message while preserving a string-or-integer request ID.
+  /// Sends a JSON-RPC message while preserving a string-or-number request ID.
   Future<void> sendWithRequestId(
     JsonRpcMessage message, {
     RequestId? relatedRequestId,
   });
 }
 
 extension RequestIdAwareTransportSend on Transport {
-  /// Sends [message] while preserving string request IDs when the transport
+  /// Sends [message] while preserving non-integer request IDs when the transport
   /// supports [RequestIdAwareTransport].
   ///
   /// Legacy transports receive only integer IDs, matching the existing public

lib/src/types/json_rpc.dart

@@ -158,18 +158,22 @@ typedef ProgressToken = dynamic;
 
 /// Parses a wire progress token.
 ///
-/// MCP progress tokens are JSON strings or integers. Reject malformed wire
+/// MCP progress tokens are JSON strings or finite numbers. Reject malformed wire
 /// shapes at decode boundaries instead of allowing dynamic values to leak into
 /// higher-level protocol code.
 ProgressToken parseProgressToken(
   Object? value, {
   String fieldName = 'progressToken',
 }) {
-  if (value is String || value is int) {
+  if (value is String) {
+    return value;
+  }
+  if (value is num && value.isFinite) {
     return value;
   }
   throw FormatException(
-    'Invalid $fieldName: expected string or integer, got ${value.runtimeType}',
+    'Invalid $fieldName: expected string or finite number, '
+    'got ${value.runtimeType}',
   );
 }
 
@@ -181,15 +185,19 @@ typedef RequestId = dynamic;
 
 /// Parses a JSON-RPC request identifier.
 ///
-/// JSON-RPC/MCP request IDs are JSON strings or integers for SDK request
+/// JSON-RPC/MCP request IDs are JSON strings or finite numbers for SDK request
 /// boundaries. Notifications omit the `id` member entirely, and responses may
 /// omit the `id` member for JSON-RPC error cases.
 RequestId parseRequestId(Object? value, {String fieldName = 'id'}) {
-  if (value is String || value is int) {
+  if (value is String) {
+    return value;
+  }
+  if (value is num && value.isFinite) {
     return value;
   }
   throw FormatException(
-    'Invalid $fieldName: expected string or integer, got ${value.runtimeType}',
+    'Invalid $fieldName: expected string or finite number, '
+    'got ${value.runtimeType}',
   );
 }
 
@@ -204,6 +212,10 @@ RequestId? _parseErrorResponseId(Map<String, dynamic> json) {
   return parseRequestId(json['id']);
 }
 
+Object _requestIdToJson(RequestId id, String fieldName) {
+  return parseRequestId(id, fieldName: fieldName);
+}
+
 final _metaPrefixLabelPattern = RegExp(
   r'^[A-Za-z](?:[A-Za-z0-9-]*[A-Za-z0-9])?$',
 );
@@ -246,9 +258,9 @@ void validateMetaKeyName(String key, {String fieldName = '_meta'}) {
 
 /// Validates request metadata that can affect protocol behavior.
 ///
-/// `_meta.progressToken` is an MCP wire token and must be a string or integer
-/// when present. [validateKeys] opts in to the MCP 2026 `_meta` key-name
-/// grammar without changing stable/legacy request parsing.
+/// `_meta.progressToken` is an MCP wire token and must be a string or finite
+/// number when present. [validateKeys] opts in to the MCP 2026 `_meta`
+/// key-name grammar without changing stable/legacy request parsing.
 Map<String, dynamic>? validateRequestMeta(
   Map<String, dynamic>? meta, {
   bool validateKeys = false,
@@ -449,7 +461,7 @@ class JsonRpcRequest extends JsonRpcMessage {
   @override
   Map<String, dynamic> toJson() => {
         'jsonrpc': jsonrpc,
-        'id': id,
+        'id': _requestIdToJson(id, 'JsonRpcRequest.id'),
         'method': method,
         if (params != null || meta != null)
           'params': <String, dynamic>{
@@ -506,7 +518,7 @@ class JsonRpcResponse extends JsonRpcMessage {
   @override
   Map<String, dynamic> toJson() => {
         'jsonrpc': jsonrpc,
-        'id': id,
+        'id': _requestIdToJson(id, 'JsonRpcResponse.id'),
         'result': <String, dynamic>{
           ...readJsonObject(result, 'JsonRpcResponse.result'),
           if (meta != null)
@@ -596,7 +608,7 @@ class JsonRpcError extends JsonRpcMessage {
   @override
   Map<String, dynamic> toJson() => {
         'jsonrpc': jsonrpc,
-        if (id != null) 'id': id,
+        if (id != null) 'id': _requestIdToJson(id, 'JsonRpcError.id'),
         'error': error.toJson(),
       };
 }

lib/src/types/misc.dart

@@ -31,7 +31,7 @@ class CancelledNotification {
       );
 
   Map<String, dynamic> toJson() => {
-        'requestId': requestId,
+        'requestId': parseRequestId(requestId, fieldName: 'requestId'),
         if (reason != null) 'reason': reason,
       };
 }
@@ -148,7 +148,7 @@ class ProgressNotification implements Progress {
 
   @override
   Map<String, dynamic> toJson() => {
-        'progressToken': progressToken,
+        'progressToken': parseProgressToken(progressToken),
         ...Progress(
           progress: progress,
           total: total,

packages/mcp_dart_cli/README.md

@@ -127,7 +127,7 @@ The CLI supports `sampling/createMessage` requests from the server (often used b
 
 ### Conformance
 
-Run built-in fixture checks, MCP 2025-11-25 spec-critical checks, and deterministic fuzz checks for MCP protocol edge cases. The fixture suite covers JSON-RPC malformed-message handling, string request IDs, string progress tokens, and advertised protocol-version support. The spec suite covers raw-wire lifecycle, capability, elicitation, task-metadata, and progress-token negative cases.
+Run built-in fixture checks, MCP 2025-11-25 spec-critical checks, and deterministic fuzz checks for MCP protocol edge cases. The fixture suite covers JSON-RPC malformed-message handling, string and numeric request IDs, string and numeric progress tokens, and advertised protocol-version support. The spec suite covers raw-wire lifecycle, capability, elicitation, task-metadata, and progress-token negative cases.
 
 ```bash
 # Run all built-in fixture cases

packages/mcp_dart_cli/lib/src/conformance_runner.dart

@@ -103,13 +103,27 @@ class ConformanceRunner {
                 'Parses and serializes successful responses with string JSON-RPC IDs.',
             check: _preservesStringResponseId,
           ),
+          _ConformanceCase(
+            suite: _fixtureSuite,
+            name: 'jsonrpc.preserves-numeric-response-id',
+            description:
+                'Parses and serializes successful responses with numeric JSON-RPC IDs.',
+            check: _preservesNumericResponseId,
+          ),
           _ConformanceCase(
             suite: _fixtureSuite,
             name: 'jsonrpc.preserves-string-progress-token',
             description:
                 'Parses and serializes progress notifications with string progress tokens.',
             check: _preservesStringProgressToken,
           ),
+          _ConformanceCase(
+            suite: _fixtureSuite,
+            name: 'jsonrpc.preserves-numeric-progress-token',
+            description:
+                'Parses and serializes progress notifications with numeric progress tokens.',
+            check: _preservesNumericProgressToken,
+          ),
           _ConformanceCase(
             suite: _fixtureSuite,
             name: 'protocol-version.advertises-latest-2025-11-25',
@@ -151,7 +165,7 @@ class ConformanceRunner {
             suite: _specSuite,
             name: 'progress.rejects-malformed-progress-token',
             description:
-                'Rejects progress notifications whose progressToken is not a string or integer.',
+                'Rejects progress notifications whose progressToken is not a string or finite number.',
             check: _rejectsMalformedProgressToken,
           ),
         ];
@@ -283,8 +297,11 @@ class _GeneratedJsonRpcFixture {
 
 _GeneratedJsonRpcFixture _generatedJsonRpcFixture(Random random, int index) {
   final numericId = random.nextInt(1000000);
+  final numericIdValue =
+      random.nextBool() ? numericId : numericId + random.nextDouble();
   final stringId = 'req-${random.nextInt(1000000)}';
-  final progressToken = random.nextBool() ? numericId : 'progress-$numericId';
+  final progressToken =
+      random.nextBool() ? numericIdValue : 'progress-$numericId';
 
   return switch (random.nextInt(6)) {
     0 => _GeneratedJsonRpcFixture(
@@ -311,28 +328,28 @@ _GeneratedJsonRpcFixture _generatedJsonRpcFixture(Random random, int index) {
       ),
     2 => _GeneratedJsonRpcFixture(
         name: 'fuzz.jsonrpc.request-id.$index',
-        description: 'Generated requests preserve string-or-integer IDs.',
+        description: 'Generated requests preserve string-or-number IDs.',
         message: <String, dynamic>{
           'jsonrpc': jsonRpcVersion,
-          'id': random.nextBool() ? numericId : stringId,
+          'id': random.nextBool() ? numericIdValue : stringId,
           'method': Method.ping,
         },
         expectation: _expectRequestIdRoundTrip,
       ),
     3 => _GeneratedJsonRpcFixture(
         name: 'fuzz.jsonrpc.response-id.$index',
-        description: 'Generated responses preserve string-or-integer IDs.',
+        description: 'Generated responses preserve string-or-number IDs.',
         message: <String, dynamic>{
           'jsonrpc': jsonRpcVersion,
-          'id': random.nextBool() ? numericId : stringId,
+          'id': random.nextBool() ? numericIdValue : stringId,
           'result': <String, dynamic>{},
         },
         expectation: _expectResponseIdRoundTrip,
       ),
     4 => _GeneratedJsonRpcFixture(
         name: 'fuzz.jsonrpc.progress-token.$index',
         description:
-            'Generated progress notifications preserve string-or-integer progress tokens.',
+            'Generated progress notifications preserve string-or-number progress tokens.',
         message: <String, dynamic>{
           'jsonrpc': jsonRpcVersion,
           'method': Method.notificationsProgress,
@@ -346,11 +363,10 @@ _GeneratedJsonRpcFixture _generatedJsonRpcFixture(Random random, int index) {
       ),
     _ => _GeneratedJsonRpcFixture(
         name: 'fuzz.jsonrpc.error-id.$index',
-        description:
-            'Generated error responses preserve string-or-integer IDs.',
+        description: 'Generated error responses preserve string-or-number IDs.',
         message: <String, dynamic>{
           'jsonrpc': jsonRpcVersion,
-          'id': random.nextBool() ? numericId : stringId,
+          'id': random.nextBool() ? numericIdValue : stringId,
           'error': <String, dynamic>{
             'code': ErrorCode.invalidRequest.value,
             'message': 'generated invalid request',
@@ -662,6 +678,24 @@ Future<void> _preservesStringResponseId() async {
   }
 }
 
+Future<void> _preservesNumericResponseId() async {
+  final message = JsonRpcMessage.fromJson(const <String, dynamic>{
+    'jsonrpc': jsonRpcVersion,
+    'id': 1.5,
+    'result': <String, dynamic>{},
+  });
+
+  if (message is! JsonRpcResponse) {
+    throw StateError('Expected JsonRpcResponse, got ${message.runtimeType}.');
+  }
+  if (message.id != 1.5) {
+    throw StateError('Expected numeric response ID to be preserved.');
+  }
+  if (message.toJson()['id'] != 1.5) {
+    throw StateError('Expected serialized response ID to stay numeric.');
+  }
+}
+
 JsonRpcResponse _expectSingleErrorFreeResponse(
   List<JsonRpcMessage> messages, {
   required RequestId id,
@@ -731,6 +765,30 @@ Future<void> _preservesStringProgressToken() async {
   }
 }
 
+Future<void> _preservesNumericProgressToken() async {
+  final message = JsonRpcMessage.fromJson(const <String, dynamic>{
+    'jsonrpc': jsonRpcVersion,
+    'method': Method.notificationsProgress,
+    'params': <String, dynamic>{
+      'progressToken': 1.5,
+      'progress': 1,
+      'total': 2,
+    },
+  });
+
+  if (message is! JsonRpcProgressNotification) {
+    throw StateError(
+      'Expected JsonRpcProgressNotification, got ${message.runtimeType}.',
+    );
+  }
+  if (message.progressParams.progressToken != 1.5) {
+    throw StateError('Expected numeric progress token to be preserved.');
+  }
+  if (message.toJson()['params']['progressToken'] != 1.5) {
+    throw StateError('Expected serialized progress token to stay numeric.');
+  }
+}
+
 Future<void> _advertisesLatestProtocolVersion() async {
   if (latestProtocolVersion != '2025-11-25') {
     throw StateError(

packages/mcp_dart_cli/test/src/conformance_command_test.dart

@@ -21,7 +21,9 @@ void main() {
           'jsonrpc.rejects-invalid-version',
           'jsonrpc.rejects-malformed-message',
           'jsonrpc.preserves-string-response-id',
+          'jsonrpc.preserves-numeric-response-id',
           'jsonrpc.preserves-string-progress-token',
+          'jsonrpc.preserves-numeric-progress-token',
           'protocol-version.advertises-latest-2025-11-25',
         ]),
       );

test/mcp_2026_07_28_test.dart

@@ -322,6 +322,26 @@ void main() {
       }
     });
 
+    test('preserves finite numeric request ids and progress tokens', () {
+      final message = JsonRpcMessage.fromJson(
+        const {
+          'jsonrpc': jsonRpcVersion,
+          'id': 1.5,
+          'method': Method.toolsList,
+          'params': {
+            '_meta': {'progressToken': 2.5},
+          },
+        },
+      );
+
+      expect(message, isA<JsonRpcListToolsRequest>());
+      final request = message as JsonRpcListToolsRequest;
+      expect(request.id, 1.5);
+      expect(request.progressToken, 2.5);
+      expect(request.toJson()['id'], 1.5);
+      expect(request.toJson()['params']['_meta']['progressToken'], 2.5);
+    });
+
     test('rejects URL elicitation relative URI values', () {
       expect(
         () => ElicitRequestParams.fromJson({

test/shared/protocol_advanced_scenarios_test.dart

@@ -103,12 +103,13 @@ void main() {
 
       // Send progress notification with an invalid progressToken type.
       transport.receiveMessage(
-        JsonRpcProgressNotification(
-          progressParams: const ProgressNotificationParams(
-            progressToken: false,
-            progress: 50,
-            total: 100,
-          ),
+        const JsonRpcNotification(
+          method: Method.notificationsProgress,
+          params: {
+            'progressToken': false,
+            'progress': 50,
+            'total': 100,
+          },
         ),
       );