Review Python

Comprehensive Python/FastAPI backend code review with optional parallel agents

Backend Code Review

Hard gates (sequence)

Advance only when each pass condition is objectively satisfied (prevents linter-owned false positives and ungrounded findings):

Gate	Pass condition
G1 — Diff scope	Step 1 command has been run; the changed .py paths are enumerated in writing (list may be empty — if empty, state that explicitly and do not invent Python findings).
G2 — Linters before manual style/type	For ruff and mypy: either no project config exists for that tool, or it was run on the changed files and you captured pass/fail (exit code or clear tool output). Do not add manual style or type findings for rules those tools already enforce when configured.
G3 — Protocol and base skills	The review-verification-protocol, python-code-review, and fastapi-code-review skills are loaded before Step 6 substantive review.
G4 — Evidence per issue	Step 7 checks are satisfied for each reported issue before it appears in the final list (re-read source, search references for “unused”, confirm framework handling for “missing”, verify syntax against current docs).
G5 — Output contract	Findings use sequential numbering, every issue has FILE:LINE, and the Verdict follows Step 8 (Critical/Major only block; Minor/Informational do not).

Arguments

• --parallel: If the agent supports subagents, run a specialized subagent per technology area (otherwise reviews run sequentially with identical output)
• Path: Target directory (default: current working directory)

Step 1: Identify Changed Files

Pass (G1): Capture the command output (or equivalent) as your authoritative changed-.py set before Steps 2–3.

bash

git diff --name-only $(git merge-base HEAD main)..HEAD | grep -E '\.py$'

Step 2: Verify Linter Status

CRITICAL: Run project linters BEFORE flagging any style or type issues. Pass (G2): You may only proceed to Step 3 after each configured linter has been run on the changed files or you have recorded why it was skipped (missing config).

bash

# Check if ruff config exists and run it
if [ -f "pyproject.toml" ] || [ -f "ruff.toml" ]; then
    ruff check <changed_files>
fi

# Check if mypy config exists and run it
if [ -f "pyproject.toml" ] || [ -f "mypy.ini" ]; then
    mypy <changed_files>
fi

Rules:

• If a linter passes for a specific rule (e.g., line length), DO NOT flag that issue manually
• Linter configuration is authoritative for style rules
• Only flag issues that linters cannot detect (semantic issues, architectural problems)

Why: Analysis of 24 review outcomes showed 4 false positives (17%) where reviewers flagged line-length violations that ruff check confirmed don't exist. The linter's configuration reflects intentional project decisions.

Step 3: Detect Technologies

bash

# Detect Pydantic-AI
grep -r "pydantic_ai\|@agent\.tool\|RunContext" --include="*.py" -l | head -3

# Detect SQLAlchemy
grep -r "from sqlalchemy\|Session\|relationship" --include="*.py" -l | head -3

# Detect Postgres-specific
grep -r "psycopg\|asyncpg\|JSONB\|GIN" --include="*.py" -l | head -3

# Check for test files
git diff --name-only $(git merge-base HEAD main)..HEAD | grep -E 'test.*\.py$'

Step 4: Load Verification Protocol

Load the review-verification-protocol skill and keep its checklist in mind throughout the review.

Step 5: Load Skills

Load each applicable skill (read its SKILL.md) before reviewing its domain.

Always load:

• python-code-review
• fastapi-code-review

Conditionally load based on detection:

Condition	Skill
Test files changed	pytest-code-review
Pydantic-AI detected	pydantic-ai-common-pitfalls
SQLAlchemy detected	sqlalchemy-code-review
Postgres detected	postgres-code-review

Step 6: Review

If the agent supports subagents, dispatch one per technology area in parallel; otherwise run the same areas sequentially, producing identical output.

Sequential (default, or when subagents are unavailable):

1. Load applicable skills
2. Review Python quality issues first
3. Review FastAPI patterns
4. Review detected technology areas
5. Consolidate findings

Parallel (--parallel flag, when the agent supports subagents):

1. Detect all technologies upfront
2. Dispatch one subagent per technology area
3. Each subagent loads its skill and reviews its domain
4. Wait for all subagents
5. Consolidate findings

Before Flagging Optimization or Pattern Issues

1. Check project conventions (e.g. AGENTS.md or CLAUDE.md) for documented intentional patterns
2. Check code comments around the flagged area for "intentional", "optimization", or "NOTE:"
3. Trace the code path before claiming missing coverage or inconsistent handling
4. Consider framework idioms - what looks wrong generically may be correct for the framework

Why: Analysis showed rejections where reviewers flagged "inconsistent error handling" that was intentional optimization, and "missing test coverage" for code paths that don't exist.

Step 7: Verify Findings

Pass (G4): No issue ships until all bullets below are true for that issue.

Before reporting any issue:

1. Re-read the actual code (not just diff context)
2. For "unused" claims - did you search all references?
3. For "missing" claims - did you check framework/parent handling?
4. For syntax issues - did you verify against current version docs?
5. Remove any findings that are style preferences, not actual issues

Step 8: Review Convergence

Pass (G5): Final markdown matches the Output Format template; verdict line reflects only Critical/Major blockers per scope rules below.

Single-Pass Completeness

You MUST report ALL issues across ALL categories (style, logic, types, tests, security, performance) in a single review pass. Do not hold back issues for later rounds.

Before submitting findings, ask yourself:

• "If all my recommended fixes are applied, will I find NEW issues in the fixed code?"
• "Am I requesting new code (tests, types, modules) that will itself need review?"

If yes to either: include those anticipated downstream issues NOW, in this review, so the author can address everything at once.

Scope Rules

• Review ONLY the code in the diff and directly related existing code
• Do NOT request new features, test infrastructure, or architectural changes that didn't exist before the diff
• If test coverage is missing, flag it as ONE Minor issue ("Missing test coverage for X, Y, Z") — do NOT specify implementation details like mock libraries, behaviour extraction, or dependency injection patterns that would introduce substantial new code
• Typespecs, documentation, and naming issues are Minor unless they affect public API contracts
• Do NOT request adding new dependencies (e.g. Mox, testing libraries, linter plugins)

Fix Complexity Budget

Fixes to existing code should be flagged at their real severity regardless of size.

However, requests for net-new code that didn't exist before the diff must be classified as Informational:

• Adding a new dependency (e.g. Mox, a linter plugin)
• Creating entirely new modules, files, or test suites
• Extracting new behaviours, protocols, or abstractions

These are improvement suggestions for the author to consider in future work, not review blockers.

Iteration Policy

If this is a re-review after fixes were applied:

• ONLY verify that previously flagged issues were addressed correctly
• Do NOT introduce new findings unrelated to the previous review's issues
• Accept Minor/Nice-to-Have issues that weren't fixed — do not re-flag them
• The goal of re-review is VERIFICATION, not discovery

Output Format

markdown

## Review Summary

[1-2 sentence overview of findings]

## Issues

### Critical (Blocking)

1. [FILE:LINE] ISSUE_TITLE
   - Issue: Description of what's wrong
   - Why: Why this matters (bug, type safety, security)
   - Fix: Specific recommended fix

### Major (Should Fix)

2. [FILE:LINE] ISSUE_TITLE
   - Issue: ...
   - Why: ...
   - Fix: ...

### Minor (Nice to Have)

N. [FILE:LINE] ISSUE_TITLE
   - Issue: ...
   - Why: ...
   - Fix: ...

### Informational (For Awareness)

N. [FILE:LINE] SUGGESTION_TITLE
   - Suggestion: ...
   - Rationale: ...

## Good Patterns

- [FILE:LINE] Pattern description (preserve this)

## Verdict

Ready: Yes | No | With fixes 1-N (Critical/Major only; Minor items are acceptable)
Rationale: [1-2 sentences]

Post-Fix Verification

After fixes are applied, run:

bash

ruff check .
mypy .
pytest

All checks must pass before approval.

Rules

• Load skills BEFORE reviewing (not after)
• Number every issue sequentially (1, 2, 3...)
• Include FILE:LINE for each issue
• Separate Issue/Why/Fix clearly
• Categorize by actual severity
• Run verification after fixes
• Report ALL issues in a single pass — do not hold back findings for later iterations
• Re-reviews verify previous fixes ONLY — no new discovery
• Requests for net-new code (new modules, dependencies, test suites) are Informational, not blocking
• The Verdict ignores Minor and Informational items — only Critical and Major block approval