Errors

All errors return a JSON body with an error string. The HTTP status is meaningful — your client should branch on it.

Error shape

{ "error": "human-readable reason" }

That's it. No error codes, no nested structures. The MCP wrapper translates these into isError: true content blocks with the same message; in REST you'll see them as the JSON body.

Status codes

200 — success. Body shape varies by tool.
400 — malformed input. Most often a required field missing or out-of-range. Body explains the specific reason.
401 — missing or invalid x-mneva-key. Check that your key is set on the request and matches an active tenant.
404 — referenced resource not found. Belief 12 not found, prediction 7 not found, tenant unknown. Body specifies which.
5xx — unexpected. Probably temporary. Mneva's tooling does not retry automatically; your client should backoff and retry idempotent reads.

Common errors

Message	What it means	What to do
`invalid or missing API key`	Header `x-mneva-key` is wrong or absent	Check `MNEVA_KEY` env. Rotate if you suspect compromise.
`prediction X not found`	The id you passed never existed, or belongs to another tenant	Confirm the id from `predictions_open` first.
`prediction X is already resolved`	You resolved this prediction once already	Predictions resolve once; query don't re-resolve.
`outcome must be one of: correct, incorrect, partial`	`outcome` value isn't one of the three	Use one of the literal strings.
`belief X is superseded`	You're trying to add evidence against a belief that has been revised	Find the current belief via `currentBeliefs` and record evidence on that one.
`kind must be 'supporting' or 'refuting'`	`evidence(kind=...)` got something else	Use the literal strings.
`prediction and domain are required`	`predict()` was called missing one	Both fields are required; domain is the calibration key.

If a 5xx is reproducible, please report it — support@mneva.dev or a GitHub issue against mneva-connect.