FastAPI: Perch rule pack
3 saved requirements for FastAPI. Inspect the selectors and adapt the example paths to your repository.
- name: tenant-scoped-update
where: "orders.py"
ensure: >-
The cancellation UPDATE must constrain tenant_id to actor.tenant_id before changing the order. An id-only or owner-only update breaks this requirement.
- name: outbox-no-early-commit
where: "confirmation.py"
ensure: >-
The order update and outbox insertion stay in the same transaction. The function must not explicitly commit inside the session.begin block before it finishes successfully.
- name: discount-limit
where: "main.py"
ensure: >-
The discount percentage accepted by the checkout endpoint must be constrained to the inclusive range 0 to 20 before a total is calculated.
Download the rule pack ZIP · Download YAML · Agent repair task · Implementation, integration requirements and captured checks
Install the rule without replacing your configuration
npm install -g @lakeday/perch
perch login
curl -fL 'https://reporules.fyi/fastapi/rule-pack.zip' -o 'perch-guide-fastapi.zip'
unzip -n 'perch-guide-fastapi.zip'Keep your existing perch.yaml. Extraction preserves existing files and adds .perch/rules/perch-guide-fastapi.yaml. Review each where selector before running a check on your application.
Configure your coding agent
perch setup claude-code
perch setup codex
perch setup cursor
perch setup piChoose the setup command for the agent you use.
Check the edit, fix the finding, check again
perch check orders.py --rules tenant-scoped-update --json
perch check confirmation.py --rules outbox-no-early-commit --json
perch check main.py --rules discount-limit --jsonRun the check after an agent edit. Read the finding and affected code, repair the implementation, and repeat the identical command. Keep the application regression tests as separate gates.
Exit 3 means a finding. Exit 1 or 2 means the check did not complete. A pass does not prove application correctness. Fresh judgments can vary; unchanged requests reuse cached answers. Relevant source is sent to the configured model service.