Black
The uncompromising Python code formatter. Black reformats Python code to a single, consistent style — no configuration debates. Its opinionated approach eliminates style discussions from code reviews, making it the most widely adopted Python formatter. Black is deterministic (same input always produces same output) and produces a subset of PEP 8 with specific line length, quoting, and whitespace rules. Note: Ruff's formatter is a compatible, faster alternative.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Local-only formatting tool — no network calls. No sensitive data exposure risk.
⚡ Reliability
Best When
You want zero-configuration Python formatting that your whole team adopts without debate — Black is the standard that most Python open-source projects use.
Avoid When
You're already using Ruff — switch to 'ruff format' (Black-compatible) rather than running two formatters. Or if you need highly customized formatting styles.
Use Cases
- • Enforce consistent Python code style across agent codebases — run Black in CI to reject non-formatted code
- • Auto-format agent-generated Python code before execution or storage — ensure generated code is clean and readable
- • Eliminate code style discussions in code review by adopting Black as the project-wide standard
- • Format Python code in pre-commit hooks to keep repository history clean and diffs focused on logic changes
- • Integrate Black with editors (VS Code, PyCharm) via extensions for format-on-save in agent development workflows
Not For
- • Teams needing custom formatting rules — Black is opinionated by design; use autopep8 if you need more configuration
- • Non-Python code formatting — Black is Python-only; use Prettier for JS/TS/CSS
- • Projects where Ruff is already in use — Ruff's formatter (ruff format) is Black-compatible and faster; no need for both
Interface
Authentication
Local CLI tool — no external auth.
Pricing
MIT-licensed open source maintained by the Python Software Foundation (PSF).
Agent Metadata
Known Gotchas
- ⚠ Black reformats magic trailing commas — a trailing comma in a function call or definition forces multi-line formatting; adding/removing trailing commas changes formatting significantly
- ⚠ --check mode returns exit code 1 when files need formatting — CI pipelines must distinguish this from actual errors; use exit code logic carefully in agent CI scripts
- ⚠ Black's line length default is 88 characters (not PEP 8's 79) — configure other tools (flake8, ruff) to match with max-line-length = 88 to avoid conflicts
- ⚠ Black formats strings to double quotes by default — single-quoted strings in existing code become double-quoted on first run; commit the initial formatting as a separate 'style: apply Black' commit
- ⚠ Black cannot format f-strings with complex expressions in Python 3.11 and earlier — very complex f-strings may cause Black to leave them unformatted with no warning
- ⚠ Running Black and isort together can conflict — use Black's --profile=black isort setting or switch to Ruff which handles both consistently
Alternatives
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Scores are editorial opinions as of 2026-03-07.