Tool errors

A tool that fails still returns HTTP 200. The result carries isError: true, a message for the model, and a machine-readable reason:

result

{
  "content": [{ "type": "text", "text": "No surface with id 9999" }],
  "structuredContent": { "reason": "SURFACE_NOT_FOUND", "message": "No surface with id 9999" },
  "isError": true
}

Reason	Meaning
`SURFACE_NOT_FOUND`	No such surface in your organization — including another org's surface.
`INVALID_ARGUMENTS`	A missing, mistyped or invalid argument; the message names it.
`PLAN_LIMIT_REACHED`	No room for another active surface on the plan; archived surfaces don't count. Carries plan, limit, used, usage_url and upgrade_url.
`MULTI_SURFACE_SOURCE`	The surface shares a content source; manage its variants in the dashboard.
`VARIANT_NOT_FOUND`	No such variant on that surface — including another surface's variant.
`SETUP_FAILED`	surface_setup failed at the step it names (structuredContent.step); nothing was created.