Every backend rule in Specter has an on_error setting: allow (fail-open, the default, so an outage never blocks genuine customers), block (fail-closed), or review. Specter also checks that a transaction carries the fields a backend needs before calling it; if fields are missing, it skips the call and tells you which ones.

Velocity counters are fail-open too: if the counter store is unavailable, the check never blocks a real customer. This keeps checkout resilient even when an external dependency degrades.

→ See backend error handling