> ## Documentation Index
> Fetch the complete documentation index at: https://docs.narrative.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Unknown MCP Tool

> The MCP server reported method-not-found (JSON-RPC -32601) for the called tool.

**Surface:** `GET /agents/runs/{id}`, `error.type = "UnknownTool"`

## When this error occurs

The workflow called an MCP server's `tools/call` for a tool name that the server doesn't
recognise. JSON-RPC reports this as `-32601 method not found`.

Discovery normally prevents this — the workflow calls `tools/list` at run start and uses only
the names the server actually exposes. This error fires when something changes between
discovery and the `tools/call`:

* The server is behind a load balancer where some instances have the tool and some don't
  (deploy in progress on the server side).
* The server's catalog was edited between the run's `tools/list` and `tools/call` (rare race;
  same-run discovery + call usually happen within a few hundred ms).
* The model hallucinated a tool name that wasn't in the discovered catalog — but in that case
  the workflow would normally reject earlier with
  [Unknown Tool Alias](./unknown-tool-alias). Seeing `UnknownTool` instead suggests a
  classifier mismatch worth investigating.

## How to fix

1. Verify the tool name against the MCP server's current `tools/list` (curl it directly with a
   JSON-RPC client) — has the catalog drifted?
2. If the discrepancy is intermittent, fix the server-side deploy first.
3. If the catalog now permanently lacks the tool the agent loop was calling, either restore the
   tool or update your system prompt to stop referencing it.