Aider

Aider is a free, open-source AI pair programming tool that lives entirely in the terminal. It was created by Paul Gauthier, previously CTO of Groupon and co-founder of Inktomi, who started building it as a side project in April 2023 and released the first public version that June. Rather than positioning itself as a fully autonomous coding agent, Aider deliberately follows a pair programming philosophy: it makes one change, waits for developer feedback, then proceeds, treating the human as an active collaborator rather than a passive approver. Released under the Apache 2.0 license, the project has grown to over 44,000 GitHub stars and 6.8 million PyPI installs, processing roughly 15 billion tokens of coding requests per week, with Aider itself now writing around 88% of the code in its own recent releases.

At the core of Aider is a tree-sitter-based repository map that uses a PageRank-style algorithm to identify the most relevant functions and classes in a project, letting it work effectively on large codebases without dumping every file into the model's context. Every change Aider makes is automatically committed to git with a descriptive, AI-generated message, so developers can diff, review, and undo AI edits using familiar git tools. Aider is model-agnostic, connecting to over 100 LLM providers through the LiteLLM routing library, including Claude, OpenAI's GPT and o-series models, DeepSeek, Gemini, and local models run via Ollama; developers bring their own API key and pay the provider directly, with no separate Aider subscription. The tool also supports voice-to-code requests, can pull in images and web pages for visual context, integrates with existing editors by watching code comments, and automatically runs linters and test suites, fixing issues it detects.

Aider is built for developers who prefer working in the terminal and want fine-grained, git-native control over AI-driven code changes, from solo builders to teams maintaining large existing codebases. The project maintains a public LLM leaderboard that benchmarks how accurately different models complete real coding tasks when paired with Aider, and it achieved state-of-the-art results on SWE-Bench and SWE-Bench Lite shortly after launch. With hundreds of community contributors and releases shipping roughly every two weeks, Aider has remained one of the most widely used terminal-based coding agents since its debut.

Aider itself is completely free and open source under the Apache 2.0 license, with no subscription, tiers, or usage limits imposed by the project. Costs come entirely from the LLM provider a developer chooses to connect: for example, Anthropic, OpenAI, or DeepSeek API usage is billed directly by that provider at its own per-token rates, or developers can run local models through Ollama at no cost at all. Because there is no Aider-specific markup or platform fee, effective cost is determined by model choice and usage volume rather than by Aider itself.