vercel/ai · error · McpError

InvalidParams

InvalidParams

Error message

Unknown host tool: ${request.params.name}

What it means

Error "Unknown host tool: ${request.params.name}" thrown in vercel/ai.

Source

Thrown at packages/harness-acp/src/v1/bridge/host-tool-mcp-server.ts:76

  server.setRequestHandler(ListToolsRequestSchema, async () => {
    if (catalogAcknowledgmentError != null) {
      throw catalogAcknowledgmentError;
    }
    const current = catalog;
    if (onListTools != null) {
      setImmediate(() => {
        void onListTools({ revision: current.revision }).catch(error => {
          catalogAcknowledgmentError = error;
        });
      });
    }
    return { tools: current.tools.map(toMCPTool) };
  });
  server.setRequestHandler(CallToolRequestSchema, async request => {
    const current = catalog;
    const tool = current.byName.get(request.params.name);
    if (tool == null) {
      throw new McpError(
        ErrorCode.InvalidParams,
        `Unknown host tool: ${request.params.name}`,
      );
    }
    const input = request.params.arguments ?? {};
    const result = await invoke({
      toolName: tool.name,
      input,
      catalogRevision: current.revision,
    });
    return toCallToolResult({ result });
  });

  return {
    server,
    updateCatalog: async ({ revision: nextRevision, tools: nextTools }) => {
      catalog = createCatalog({
        revision: nextRevision,

View on GitHub (pinned to 69428b1f8b)

When it happens

Trigger: Thrown at packages/harness-acp/src/v1/bridge/host-tool-mcp-server.ts:76 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/95910585433ec5ca. Report an issue: GitHub.