Aider

Aider is an open-source command-line tool that pairs a large language model with git-aware editing: it maps model output to concrete file changes, commits logical units of work, and lets developers steer multi-turn coding sessions from the terminal. It is a favorite for engineers who live in vim-style workflows or CI-assisted refactors.

It supports many providers and models via configuration, maps repository structure into prompts efficiently, and emphasizes repeatable, reviewable diffs rather than opaque IDE magic. Typical uses include test-driven changes, dependency upgrades, and cross-cutting cleanups.

The software itself is free; you pay only for model API usage. Because it can modify many files autonomously, run it in repositories you trust, inspect git diff frequently, and keep backups or branches for risky tasks.