flake8

What does it do?

Flake8 checks Python code against established style rules and scans for likely bugs, then reports back a list of exact locations and descriptions of problems, without changing anything itself. Picture a grammar checker for code: it doesn’t rewrite your sentences, it just flags that a variable is never used so a human can decide what to do about it. Under the hood, it’s actually a wrapper that bundles together several separate checking tools into one combined report. It’s been a default choice in Python projects for well over a decade.

See it in action

This is a terminal command that scans a folder of Python code and lists the exact file, line, and style or bug problem it finds, like an unused import.

flake8 my_project/

# Example output:
# my_project/app.py:12:1: F401 'os' imported but unused

Why would a non-developer care?

Code that’s been through a linter like this tends to have fewer sneaky bugs, unused variables, undefined names, inconsistent spacing that hides real errors, which indirectly means the software you use built on well-linted code is more likely to behave the way it’s supposed to.

Real-world examples

Flake8 has been a standard part of Python development workflows since the early 2010s and is still specified in the automated checks of countless open-source projects. It’s often the first linter developers ever configure, precisely because of how long it’s been the community default.

Who uses it

Python teams wanting a well-established, minimal-fuss way to catch style violations and simple bugs before code gets reviewed or merged.

How it compares to alternatives

It’s less aggressive than pylint, which digs deeper into code structure and design issues, and it’s increasingly being displaced by the much faster Ruff, which reimplements most of what Flake8 checks for.