Failure modes & fail-closed - Claros

The default is fail closed on writes, open on reads: an unchecked write is the failure Claros exists to prevent.

Situation	Write	Read
Claros unreachable, error, or key rejected	Blocked: “Claros couldn’t check this action (…), so it was not run. Ask a person to confirm it is allowed before trying again.”	Passes
Check slower than `--timeout` (5 s)	Blocked, same message	Passes
A record read (`need`) fails	Blocked	Passes
The judge gives no verdict on a stop-level rule	`ask`	—
The judge can’t tell	`ask` on stop / ask rules, `nudge` on nudge rules	—
A nudge rule is broken	Forwarded; the nudge is attached to the result	—
No map governs the action	Allowed, logged `unmapped` for review	—
The tool is mapped to no workflow (Not ours)	Allowed	—
Call outside the mapping’s `when`	Allowed, logged	—

--fail-open (MCP guard), failOpen (Playwright) and fail_open (browser-use) forward writes when Claros can’t be reached. Use it only where a missed check is cheaper than a blocked action.

Unmapped writes are allowed

A write no map governs is allowed today, so a new tool doesn’t block work before an editor has looked at it. It shows up on Tools and in the check log as unmapped. Review it there.

Latency

Precise rules: milliseconds on the server. A check that reaches a fuzzy rule waits for the judge (about 1 to 2 s in our runs; budget 4.5 s). A record read adds a round trip to the app per need.