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Fix: Non-existent tool, disabled tool and inputSchema validation return MCP protocol level instead of CallToolResult with isError: true #1044

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Merged
merged 6 commits into from
Oct 28, 2025
+150 −116
Merged

Fix: Non-existent tool, disabled tool and inputSchema validation return MCP protocol level instead of CallToolResult with isError: true #1044

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efd901a
Non-existing tool, disabled tool and tool inputSchema validation retu…
KKonstantinov Oct 24, 2025
8705e69
Merge branch 'main' into bugfix/tool-validation-not-jsonrpc-error
KKonstantinov Oct 25, 2025
a0fce2a
Merge branch 'main' into bugfix/tool-validation-not-jsonrpc-error
KKonstantinov Oct 28, 2025
2cc4918
Merge branch 'main' into bugfix/tool-validation-not-jsonrpc-error
KKonstantinov Oct 28, 2025
f02ff1a
outputSchema fix - return CallToolResult on structuredContent not ret…
KKonstantinov Oct 28, 2025
98a69ba
prettier fix
KKonstantinov Oct 28, 2025
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10 changes: 1 addition & 9 deletions package-lock.json
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142 changes: 92 additions & 50 deletions src/server/mcp.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -928,37 +928,53 @@ describe('tool()', () => {

await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);

await expect(
client.request(
{
method: 'tools/call',
params: {
const result = await client.request(
{
method: 'tools/call',
params: {
name: 'test',
arguments: {
name: 'test',
arguments: {
name: 'test',
value: 'not a number'
}
value: 'not a number'
}
},
CallToolResultSchema
)
).rejects.toThrow(/Invalid arguments/);
}
},
CallToolResultSchema
);

await expect(
client.request(
expect(result.isError).toBe(true);
expect(result.content).toEqual(
expect.arrayContaining([
{
method: 'tools/call',
params: {
name: 'test (new api)',
arguments: {
name: 'test',
value: 'not a number'
}
type: 'text',
text: expect.stringContaining('Input validation error: Invalid arguments for tool test')
}
])
);

const result2 = await client.request(
{
method: 'tools/call',
params: {
name: 'test (new api)',
arguments: {
name: 'test',
value: 'not a number'
}
},
CallToolResultSchema
)
).rejects.toThrow(/Invalid arguments/);
}
},
CallToolResultSchema
);

expect(result2.isError).toBe(true);
expect(result2.content).toEqual(
expect.arrayContaining([
{
type: 'text',
text: expect.stringContaining('Input validation error: Invalid arguments for tool test (new api)')
}
])
);
});

/***
Expand Down Expand Up @@ -1152,14 +1168,24 @@ describe('tool()', () => {
await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);

// Call the tool and expect it to throw an error
await expect(
client.callTool({
name: 'test',
arguments: {
input: 'hello'
const result = await client.callTool({
name: 'test',
arguments: {
input: 'hello'
}
});

expect(result.isError).toBe(true);
expect(result.content).toEqual(
expect.arrayContaining([
{
type: 'text',
text: expect.stringContaining(
'Output validation error: Tool test has an output schema but no structured content was provided'
)
}
})
).rejects.toThrow(/Tool test has an output schema but no structured content was provided/);
])
);
});
/***
* Test: Tool with Output Schema Must Provide Structured Content
Expand Down Expand Up @@ -1274,14 +1300,22 @@ describe('tool()', () => {
await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);

// Call the tool and expect it to throw a server-side validation error
await expect(
client.callTool({
name: 'test',
arguments: {
input: 'hello'
const result = await client.callTool({
name: 'test',
arguments: {
input: 'hello'
}
});

expect(result.isError).toBe(true);
expect(result.content).toEqual(
expect.arrayContaining([
{
type: 'text',
text: expect.stringContaining('Output validation error: Invalid structured content for tool test')
}
})
).rejects.toThrow(/Invalid structured content for tool test/);
])
);
});

/***
Expand Down Expand Up @@ -1552,17 +1586,25 @@ describe('tool()', () => {

await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);

await expect(
client.request(
const result = await client.request(
{
method: 'tools/call',
params: {
name: 'nonexistent-tool'
}
},
CallToolResultSchema
);

expect(result.isError).toBe(true);
expect(result.content).toEqual(
expect.arrayContaining([
{
method: 'tools/call',
params: {
name: 'nonexistent-tool'
}
},
CallToolResultSchema
)
).rejects.toThrow(/Tool nonexistent-tool not found/);
type: 'text',
text: expect.stringContaining('Tool nonexistent-tool not found')
}
])
);
});

/***
Expand Down
114 changes: 57 additions & 57 deletions src/server/mcp.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -126,73 +126,55 @@ export class McpServer {

this.server.setRequestHandler(CallToolRequestSchema, async (request, extra): Promise<CallToolResult> => {
const tool = this._registeredTools[request.params.name];
if (!tool) {
throw new McpError(ErrorCode.InvalidParams, `Tool ${request.params.name} not found`);
}

if (!tool.enabled) {
throw new McpError(ErrorCode.InvalidParams, `Tool ${request.params.name} disabled`);
}

let result: CallToolResult;

if (tool.inputSchema) {
const parseResult = await tool.inputSchema.safeParseAsync(request.params.arguments);
if (!parseResult.success) {
throw new McpError(
ErrorCode.InvalidParams,
`Invalid arguments for tool ${request.params.name}: ${parseResult.error.message}`
);
try {
if (!tool) {
throw new McpError(ErrorCode.InvalidParams, `Tool ${request.params.name} not found`);
}

const args = parseResult.data;
const cb = tool.callback as ToolCallback<ZodRawShape>;
try {
result = await Promise.resolve(cb(args, extra));
} catch (error) {
result = {
content: [
{
type: 'text',
text: error instanceof Error ? error.message : String(error)
}
],
isError: true
};
}
} else {
const cb = tool.callback as ToolCallback<undefined>;
try {
result = await Promise.resolve(cb(extra));
} catch (error) {
result = {
content: [
{
type: 'text',
text: error instanceof Error ? error.message : String(error)
}
],
isError: true
};
if (!tool.enabled) {
throw new McpError(ErrorCode.InvalidParams, `Tool ${request.params.name} disabled`);
}
}

if (tool.outputSchema && !result.isError) {
if (!result.structuredContent) {
throw new McpError(
ErrorCode.InvalidParams,
`Tool ${request.params.name} has an output schema but no structured content was provided`
);
if (tool.inputSchema) {
const cb = tool.callback as ToolCallback<ZodRawShape>;
const parseResult = await tool.inputSchema.safeParseAsync(request.params.arguments);
if (!parseResult.success) {
throw new McpError(
ErrorCode.InvalidParams,
`Input validation error: Invalid arguments for tool ${request.params.name}: ${parseResult.error.message}`
);
}

const args = parseResult.data;

result = await Promise.resolve(cb(args, extra));
} else {
const cb = tool.callback as ToolCallback<undefined>;
result = await Promise.resolve(cb(extra));
}

// if the tool has an output schema, validate structured content
const parseResult = await tool.outputSchema.safeParseAsync(result.structuredContent);
if (!parseResult.success) {
throw new McpError(
ErrorCode.InvalidParams,
`Invalid structured content for tool ${request.params.name}: ${parseResult.error.message}`
);
if (tool.outputSchema && !result.isError) {
if (!result.structuredContent) {
throw new McpError(
ErrorCode.InvalidParams,
`Output validation error: Tool ${request.params.name} has an output schema but no structured content was provided`
);
}

// if the tool has an output schema, validate structured content
const parseResult = await tool.outputSchema.safeParseAsync(result.structuredContent);
if (!parseResult.success) {
throw new McpError(
ErrorCode.InvalidParams,
`Output validation error: Invalid structured content for tool ${request.params.name}: ${parseResult.error.message}`
);
}
}
} catch (error) {
return this.createToolError(error instanceof Error ? error.message : String(error));
}

return result;
Expand All @@ -201,6 +183,24 @@ export class McpServer {
this._toolHandlersInitialized = true;
}

/**
* Creates a tool error result.
*
* @param errorMessage - The error message.
* @returns The tool error result.
*/
private createToolError(errorMessage: string): CallToolResult {
return {
content: [
{
type: 'text',
text: errorMessage
}
],
isError: true
};
}

private _completionHandlerInitialized = false;

private setCompletionRequestHandler() {
Expand Down