Errors
The MCP returns standard JSON-RPC error responses. The most common ones:
Auth errors
| When | Code | Meaning |
|---|---|---|
Missing Authorization header on /mcp/feedback | 401 + WWW-Authenticate | The auth-walled URL requires an OAuth Bearer token with at least mcp:read. Read-only callers should use /mcp instead, which has no auth. |
Invalid or expired Bearer JWT on /mcp/feedback | 401 | Token expired or signature invalid. The OAuth client should refresh; if refresh fails, re-consent at RL feedback. |
| Revoked refresh token | -32001 | A revoked refresh chain triggers chain-wide revocation per OAuth 2.1. Re-consent at RL feedback. |
Tool errors
| When | Code | Meaning |
|---|---|---|
| Unknown tool name | -32601 | Method not found. Check tools/list for the exact name. |
| Invalid parameters | -32602 | One of your parameters failed zod validation. The error message names the offending field. |
| Standard not found | (no error — empty result) | get_standard and friends return { found: false } rather than 404. |
For other errors, the JSON-RPC body's error.message field contains a human-readable explanation.