Tool results

Every completed process returns text content and a machine-readable structuredContent object.

{
  "exitCode": 0,
  "stdout": "rustc 1.98.1\n",
  "stderr": "",
  "timedOut": false,
  "stdoutTruncated": false,
  "stderrTruncated": false
}

Fields

Field	Type	Meaning
exitCode	integer or null	Native child exit status; may be null when no code is available
stdout	string	Captured standard output, converted lossily to UTF-8 if necessary
stderr	string	Captured standard error, converted lossily to UTF-8 if necessary
timedOut	boolean	Whether the configured deadline terminated the process
stdoutTruncated	boolean	Whether stdout exceeded its byte limit
stderrTruncated	boolean	Whether stderr exceeded its byte limit

The output byte limit applies independently to each stream. The process continues to be drained after the cap so a full pipe cannot deadlock it.

Success and errors

A call succeeds only when exitCode is 0 and timedOut is false. On success, primary text content is stdout. On failure, text content includes a summary of exit status, timeout, stdout, and stderr, and MCP isError is true.

Validation, policy, spawn, concurrency, and rate-limit failures also return a structured error with exitCode: null and the message in stderr.

Cancellation

For synchronous calls, MCP cancellation terminates the owned child process tree and suppresses a late response. For task calls, cancellation persists a terminal task state that clients can retrieve later.