Black

Overview

Black is a free, MIT-licensed formatter for Python code, aimed at developers and teams that want one shared style without maintaining a long list of formatting preferences. Its strongest case is consistency backed by a syntax-equivalence check; its command-line orientation and fixed style make it a less suitable fit for custom house rules or software that needs a Python library interface.

Key features

Black reformats complete files in place, using an 88-character default line length. That whole-file approach gives projects a uniform result, but it is not a tool for formatting only changed lines. Black says its small diffs can help speed code review, and it checks that a rewrite leaves an effectively equivalent abstract syntax tree, raising an error if that check fails.

The tradeoff is deliberate rigidity. Black does not let users configure indentation style, so teams that need to preserve another convention should choose a formatter with more control. For stable releases, formatting remains unchanged between releases in the same calendar year when options are held constant, reducing the risk of style churn during upgrades.

Jupyter Notebook formatting is available by installing the jupyter extra, though Black skips cells with automagics, non-Python or multiline magics, transformed magic code, or invalid syntax. It also provides blackd, an HTTP server that binds to localhost by default, official Docker images tagged for releases and prereleases, and a GitHub Actions integration for GitHub-hosted runner operating systems.

Pricing

Black costs nothing and is distributed under the MIT License. The free plan is the formatter itself; there is no free trial or paid plan to weigh against it. That makes it a straightforward choice for teams seeking an open-source Python formatter rather than a commercial support arrangement.

Platforms

Black runs on Linux, macOS, and Windows, and can be self-hosted. It installs with pip and requires Python 3.10 or newer to run; Black promises support for Python versions that have not reached end of life, both for running the formatter and formatting code. Its documented integrations cover editors and IDEs including Emacs, PyCharm, IntelliJ IDEA, Vim, Neovim, Visual Studio Code, and Sublime Text, as well as source version control and doctest formatting. The local HTTP server and Docker images give teams additional deployment options, but Black remains fundamentally a command-line tool and has no Python interface.

Who it's for

Black suits Python developers who value uniform output across a project more than individual formatting preferences, and teams that want formatting available through common editors or CI. It is less compelling for users who require an embeddable Python API, configurable indentation, or uninterrupted formatting of notebook cells containing unsupported magic syntax.

Pros and cons

Pros: A single style and 88-character default line length reduce formatting debates across projects.

Pros: The abstract syntax tree check catches cases where a formatting pass fails its equivalence test.

Pros: Free, MIT-licensed use is paired with documented editor, IDE, CI, Docker, and notebook support.

Cons: No indentation-style setting means teams cannot adapt Black to a different indentation convention.

Cons: Whole-file rewriting and the lack of a Python interface limit its fit for changed-lines workflows or library integrations.

Cons: Notebook cells with certain magic commands or invalid syntax are skipped.

Alternatives

For other languages or project types, Code Formatting Tools is the broader category to explore. Choose Prettier when you want an open-source formatter with API, extension, web, and desktop platform support; it also offers enterprise support and maintenance through Tidelift Subscription. rustfmt is the free option to consider for Rust, while Biome is aimed at web projects.

Choose gofmt if you want a free command-line formatter included with a Go installation. Scalafmt is the free alternative for Scala, and Taplo is another free formatter with API and extension platforms. Dart pub and Accessibility Test Framework for Android are listed as alternatives.

Verdict

Choose Black if your Python project needs a free, consistent formatter with a safety check and broad documented editor integration. Its fixed style is the main reason to look elsewhere: teams that need configurable indentation or a Python library API should pick a more adaptable tool.