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fix: correct error handling for unknown tools and resources (#1389)

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Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com>
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Anthony 2026-03-09 19:17:09 +01:00 • committed by GitHub
commit 108f2f3ab6
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5 changed files with 123 additions and 23 deletions
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15
.changeset/fix-unknown-tool-protocol-error.md Normal file
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@ -0,0 +1,15 @@
---
"@modelcontextprotocol/core": minor
"@modelcontextprotocol/server": major
---
Fix error handling for unknown tools and resources per MCP spec.
**Tools:** Unknown or disabled tool calls now return JSON-RPC protocol errors with
code `-32602` (InvalidParams) instead of `CallToolResult` with `isError: true`.
Callers who checked `result.isError` for unknown tools should catch rejected promises instead.
**Resources:** Unknown resource reads now return error code `-32002` (ResourceNotFound)
instead of `-32602` (InvalidParams).
Added `ProtocolErrorCode.ResourceNotFound`.

2
packages/client/test/client/authExtensions.test.ts
View file

@ -305,7 +305,7 @@ describe('createPrivateKeyJwtAuth', () => {
const params = new URLSearchParams();
await expect(addClientAuth(new Headers(), params, 'https://auth.example.com/token', undefined)).rejects.toThrow(
/Invalid character/
/cannot be part of a valid base64|Invalid character/
);
});

1
packages/core/src/types/types.ts
View file

@ -233,6 +233,7 @@ export enum ProtocolErrorCode {
InternalError = -32_603,
// MCP-specific error codes
ResourceNotFound = -32_002,
UrlElicitationRequired = -32_042
}

18
packages/server/src/server/mcp.ts
View file

@ -166,15 +166,15 @@ export class McpServer {
);
this.server.setRequestHandler('tools/call', async (request, ctx): Promise<CallToolResult | CreateTaskResult> => {
try {
const tool = this._registeredTools[request.params.name];
if (!tool) {
throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} not found`);
}
if (!tool.enabled) {
throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} disabled`);
}
const tool = this._registeredTools[request.params.name];
if (!tool) {
throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} not found`);
}
if (!tool.enabled) {
throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} disabled`);
}
try {
const isTaskRequest = !!request.params.task;
const taskSupport = tool.execution?.taskSupport;
const isTaskHandler = 'createTask' in (tool.handler as AnyToolHandler<AnySchema>);
@ -506,7 +506,7 @@ export class McpServer {
}
}
throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Resource ${uri} not found`);
throw new ProtocolError(ProtocolErrorCode.ResourceNotFound, `Resource ${uri} not found`);
});
this._resourceHandlersInitialized = true;

110
test/integration/test/server/mcp.test.ts
View file

@ -1777,22 +1777,59 @@ describe('Zod v4', () => {
await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
const result = await client.request({
method: 'tools/call',
params: {
name: 'nonexistent-tool'
}
await expect(
client.request({
method: 'tools/call',
params: {
name: 'nonexistent-tool'
}
})
).rejects.toMatchObject({
code: ProtocolErrorCode.InvalidParams,
message: expect.stringContaining('nonexistent-tool')
});
});
/***
* Test: ProtocolError for Disabled Tool
*/
test('should throw ProtocolError for disabled tool', async () => {
const mcpServer = new McpServer({
name: 'test server',
version: '1.0'
});
expect(result.isError).toBe(true);
expect(result.content).toEqual(
expect.arrayContaining([
const client = new Client({
name: 'test client',
version: '1.0'
});
const tool = mcpServer.registerTool('test-tool', {}, async () => ({
content: [
{
type: 'text',
text: expect.stringContaining('Tool nonexistent-tool not found')
text: 'Test response'
}
])
);
]
}));
tool.disable();
const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
await expect(
client.request({
method: 'tools/call',
params: {
name: 'test-tool'
}
})
).rejects.toMatchObject({
code: ProtocolErrorCode.InvalidParams,
message: expect.stringContaining('disabled')
});
});
/***
@ -2797,7 +2834,51 @@ describe('Zod v4', () => {
uri: 'test://nonexistent'
}
})
).rejects.toThrow(/Resource test:\/\/nonexistent not found/);
).rejects.toMatchObject({
code: ProtocolErrorCode.ResourceNotFound,
message: expect.stringContaining('not found')
});
});
/***
* Test: ProtocolError for Disabled Resource
*/
test('should throw ProtocolError for disabled resource', async () => {
const mcpServer = new McpServer({
name: 'test server',
version: '1.0'
});
const client = new Client({
name: 'test client',
version: '1.0'
});
const resource = mcpServer.registerResource('test', 'test://resource', {}, async () => ({
contents: [
{
uri: 'test://resource',
text: 'Test content'
}
]
}));
resource.disable();
const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
await expect(
client.request({
method: 'resources/read',
params: {
uri: 'test://resource'
}
})
).rejects.toMatchObject({
code: ProtocolErrorCode.InvalidParams,
message: expect.stringContaining('disabled')
});
});
/***
@ -3693,7 +3774,10 @@ describe('Zod v4', () => {
name: 'nonexistent-prompt'
}
})
).rejects.toThrow(/Prompt nonexistent-prompt not found/);
).rejects.toMatchObject({
code: ProtocolErrorCode.InvalidParams,
message: expect.stringContaining('not found')
});
});
/***