fettle: Command for Claude Code

$ARGUMENTS refers to any text the user typed after the slash command.

Run a pre-deployment FMEA (Failure Mode and Effects Analysis) quality checklist for the target service.

Procedure

1. Determine service name. Use $ARGUMENTS if provided. If not provided, derive the name from the current working directory basename.

2. Create output directory. Create .fettle/ in the current working directory if it doesn't already exist:

   mkdir -p .fettle
   

3. Copy the preflight template. Locate the bundled template and write it to .fettle/preflight-{name}.md, replacing {SERVICE_NAME} with the service name and {DATE} with today's date:

   python3 -c "from fettle._resources import templates_dir; print(templates_dir() / 'preflight.md')"
   

   Read the file at the printed path.

4. Run automated checks on the codebase. Use Grep and Glob to scan for known anti-patterns and pre-fill the template sections:

   Time Model (Section 1):

   • Search for datetime.now across all Python files. Any hit is a [FAIL] — record file:line.
   • Search for datetime.utcnow as well (deprecated in Python 3.12+). Any hit is a [FAIL].
   • If no hits, mark as [PASS].

   Error Handling (Section 2):

   • Search for except.*:.*pass or bare except: patterns. Any hit is a [FAIL] — record file:line.
   • Search for AsyncClient (or httpx.Client, requests.get, requests.post) without timeout on the same line or within 5 lines. Flag as [FAIL] if timeout is missing.
   • If no hits, mark as [PASS].

   LLM Output Parsing (Section 3):

   • Search for re.search, re.findall, re.match patterns that appear to parse LLM output (look in pipeline/, agents/, or similar directories). Any hit is a [FAIL] — record file:line.
   • If no hits, mark as [PASS].

   Data Persistence (Section 4):

   • Search for .write_text( or .write_bytes( on paths that are NOT in /tmp or using tempfile. Flag as [?] for manual review with file:line.
   • Search for absence of atomic write patterns (no tempfile + rename/replace pattern). Flag as [?].

   External Dependencies (Section 5):

   • Search for HTTP client instantiations without explicit timeout. Flag as [FAIL] with file:line.
   • Mark remaining items as [?] for manual review.

   Resource Lifecycle (Section 6):

   • Search for open( without a with statement context manager. Flag as [?] with file:line.
   • Mark as [?] for manual review.

   Observability (Section 7):

   • Search for logging. or logger. or structlog usage. If found, mark as [PASS]. If absent, mark as [FAIL].
   • Mark remaining items as [?].

   Testing Coverage (Section 8):

   • Count test files matching test_*.py or *_test.py using Glob.
   • Count total test functions (def test_) using Grep.
   • Pre-fill {TEST_COUNT} and {TEST_FILES} in the template.
   • If zero test files, mark as [FAIL]. Otherwise mark as [?] for manual assessment of coverage quality.

5. Fill the summary table. For each section, set the status based on findings:

   • PASS — all auto-checks passed and no issues found
   • FAIL — at least one auto-detected issue
   • REVIEW — needs manual inspection (items marked [?])

6. Write the completed checklist to .fettle/preflight-{name}.md.

7. Present the results to the user. Show:

   • A summary of auto-detected issues (with file:line references)
   • The overall pass/fail count
   • Which sections still need manual review ([?] items)

8. Ask the user to review and complete any remaining [?] items.

9. Suggest running the full automated scan:

   fettle check --all