HOOK · Cursor docs

Fail-closed gates (failClosed)

Hooks fail open by default. Set failClosed: true so a crashing or timed-out verification hook blocks instead of silently passing.

proof: logs blocks: verification hook silently failing open

https://cursor.com/docs/agent/hooks
Checked 2026-10-16. Read the original before installing.

Harness	Status	How
Cursor	native	failClosed: true on the hook definition.
Claude Code	adapted	Claude Code equivalent: onFailure: "block" (see entry).
Grok Build	adapted	Grok Build hooks are fail-open on crash or timeout per docs; keep the gate itself simple and exit 2 explicitly.
Codex	untested	Untested.
AGENTS.md generic	unsupported	Harness feature.

"source" = the source targets it; "untested" = not verified by ProofOfDone yet.