Aider

Aider is an open-source AI pair programming tool that runs entirely in your terminal and edits code directly in your local Git repository. Instead of replacing your editor, it works alongside your existing command-line and Git workflow: you add the files you want to change, describe the change in plain English, and Aider writes the edits across one or more files and commits each change to Git with a sensible, descriptive commit message. Because every edit is a normal Git commit, you can diff, review, undo, or revert anything the AI does using the Git tools you already use. A defining feature is its repository map, which uses tree-sitter parsing to build a PageRank-ranked index of your whole codebase - function signatures, class definitions, and cross-file references - so the model understands how a large project fits together without loading every file into context. Aider is fully model-agnostic: through LiteLLM it connects to almost any LLM, including Anthropic's Claude, OpenAI's GPT and o-series, DeepSeek, Google Gemini, xAI Grok, and local models run via Ollama, so you bring your own API key and switch providers based on cost or capability. Its Architect mode pairs an expensive reasoning model for planning with a cheaper model for the actual file edits to lower session cost. Beyond core editing, Aider supports 100+ programming languages, can lint and test code automatically and fix the problems it finds, accepts images and web pages as context, offers voice-to-code, and integrates with editors such as VS Code, JetBrains, Vim, and Emacs through its --watch mode and in-code 'AI?' comments. Created in 2023 by independent developer Paul Gauthier and released under the Apache 2.0 license, Aider has grown to 44,000+ GitHub stars and 6.8 million installs, and also maintains the widely cited Aider polyglot leaderboard for benchmarking how well LLMs edit code. It is free to use - the only cost is the token spend on whichever model provider you choose.