Black

Black is a Python formatter for developers and teams who want a shared style enforced across files, editors, and automation. It favors predictable formatting over fine-grained control: accept its rules and it can simplify routine style decisions; need custom indentation or a Python library interface and it is a poor fit.

Overview

Black follows PEP 8 and reformats complete files in place, using an 88-character default line length. Its limited style choices are a practical way to reduce formatting debates across a project, but they also mean teams cannot use it to preserve every existing convention. In particular, indentation style cannot be configured.

Black aims to keep diffs small, which can make formatting changes easier to review. It also checks that the reformatted code has an effectively equivalent abstract syntax tree and raises an error if that check fails. Stable releases are intended to produce unchanged formatting across releases in the same calendar year when the same options are used, helping limit style churn within that period.

Key features

• Whole-file formatting: Black applies its style to full files rather than only changed lines. This suits projects seeking uniform output, though it may create a broader formatting change than a changed-lines workflow.
• Editor and automation integrations: Documented integrations cover editors including Emacs, PyCharm and IntelliJ IDEA, Vim, Neovim, Visual Studio Code, and Sublime Text, as well as GitHub Actions, source version control, and doctest formatting. This makes Black usable in both local editing and automated project workflows.
• Notebook formatting: Installing Black with the jupyter extra enables Jupyter Notebook formatting. It skips cells with automagics, non-Python or multiline magics, transformed magic code, or invalid syntax, so notebooks that rely on those cells may not be fully formatted.
• Local service and containers: The included blackd HTTP server binds to localhost by default, and official Docker images are available with release and prerelease tags. These options support local service or container-based workflows without changing Black's command-line orientation.

Pricing

Black is free: its plan costs nothing and is an MIT-licensed open-source Python formatter. There is no paid tier or free trial to weigh against it; the trade-off is functional rather than commercial. Black requires Python 3.10 or newer to run, and it does not provide a Python interface, so teams wanting a library API must choose another approach.

Platforms

Black supports Windows, macOS, and Linux, and can be installed with pip. Its local HTTP server and Docker images extend deployment options, while editor integrations connect it to common development environments. Black promises support for Python versions that have not reached end of life, both for running the formatter and formatting code.

Who it's for

Black is best for Python projects that value a consistent, low-debate style and want formatting integrated into editors or CI. It is less suitable for teams that need configurable indentation, a Python library API, or notebook formatting that handles every kind of magic cell. Its MIT license and zero price also make it straightforward to adopt across projects without a subscription decision.

Pros and cons

• Pro: A consistent style and whole-file formatting reduce project-by-project formatting choices.
• Pro: The abstract-syntax-tree equivalence check can catch a formatting result that is not effectively equivalent.
• Pro: Editor, GitHub Actions, version-control, and doctest integrations support use beyond a standalone command.
• Con: No indentation-style setting means teams cannot adapt Black to a different indentation convention.
• Con: The command-line focus and lack of a Python interface limit use as an imported formatting library.
• Con: Notebook cells using certain magics or invalid syntax are skipped, leaving some notebook content outside its formatting pass.

Alternatives

For a directory of code formatting tools, start with the broader category. Choose Prettier instead if you need a free formatter with API, extension, web, and desktop-platform availability; its listed plan is free, with enterprise support and maintenance offered through Tidelift Subscription. Ruff is another free option for readers comparing tools in the Python ecosystem; its maker describes its tools as open source and permissively licensed.

Accessibility Test Framework for Android is a free alternative for readers looking at an Android accessibility test framework rather than a Python formatter. rustfmt is a free formatter option for Rust projects. Biome is a free open-source toolchain for web projects. CSharpier offers free opinionated formatting for C# and XML and installs as a .NET tool. dprint is a free MIT-licensed CLI with self-managed installation. gofmt is a free command-line formatter included with Go.

Verdict

Choose Black if your Python project wants consistent formatting enforced across whole files, with editor and automation integrations and a syntax-equivalence check. Its clearest reason to look elsewhere is the same design choice that makes it dependable: Black does not bend to custom indentation, and it offers no Python library API.