What it is
Aider is AI pair programming in your terminal. Its GitHub repository Aider-AI/aider has 49,596 stars (checked 2026-10-17) and describes it as exactly that: an AI pair programmer that lives in your command line. You launch Aider inside a project, tell it what to change in plain language, and it edits your files directly — then commits the changes to git with sensible commit messages so you can diff, manage, and undo them with familiar git tools. Unlike a browser chatbot, Aider maps your entire codebase, works with over 100 programming languages, and can lint and test your code after every change. If you want a terminal tool that edits real files, Aider is one of the most practical places to start.
Who it is for / SMB use case
Aider is for small businesses with at least one person who works in a terminal and a git repository — a solo developer, a freelancer, or a tiny dev team maintaining a website or internal tool. It is not a tool for non-technical staff: everything happens on the command line. Practical SMB use cases include:
- Feature work on an existing codebase: add a form field, a validation rule, or a new page, with Aider editing the right files and committing the result.
- Bug fixes: paste an error, point Aider at the failing file, and let it propose a fix you review before keeping.
- Refactoring and tests: split a long function, rename consistently across files, or add test cases, then run your linter and test suite on the result.
The git integration is the reason Aider suits real work: every change is a commit you can inspect and undo — safer than copy-pasting code out of a chat window.
Installation
Aider runs on macOS, Windows, and Linux. The README’s Getting Started flow installs it with the aider-install helper:
python -m pip install aider-install aider-install
Then change directory into your codebase:
cd /to/your/project
Launch Aider with the model you want to use, passing your API key on the command line. The README gives three examples:
# DeepSeek aider --model deepseek --api-key deepseek=YOUR_KEY_HERE # Claude 3.7 Sonnet aider --model sonnet --api-key anthropic=YOUR_KEY_HERE # o3-mini aider --model o3-mini --api-key openai=YOUR_KEY_HERE
Aider works best with Claude 3.7 Sonnet, DeepSeek R1 and Chat V3, and OpenAI o1, o3-mini, and GPT-4o, per the README, but it can connect to almost any LLM, including local models. For a persistent setup, store your key in an environment variable or config file — see the Aider installation guide for the full options.
How to use
Step 1: Launch Aider with the files you want to change
Run Aider with the source files you want to edit. Those files are added to the chat session, so the model can see their contents and edit them:
aider app.py utils.py
If pip did not place aider on your path, invoke it as python -m aider.main app.py utils.py. You can also launch aider anywhere in a git repo without naming files. Be selective: add only the files the change needs — unrelated files confuse the model and cost more tokens.
Step 2: Ask for one change in plain language
Type your request as a normal sentence, for example: “Add email format validation to the signup form in app.py and show a clear error message when it fails.” Aider will edit the files, then commit the change with a sensible message. Start with one small change and verify it before asking for the next.
Step 3: Manage files with in-chat commands
Aider supports commands inside the chat, all starting with /. The most useful ones are:
/add filename— add matching files to the chat session, including image files./drop filename— remove matching files from the chat session./diff— display the diff of the last Aider commit./undo— undo the last git commit if it was done by Aider./run command— run a shell command and optionally add the output to the chat./voice— speak to Aider to request code changes with your voice./help— show help about all commands.
Use /diff after every change and /undo the moment a change looks wrong. Those two commands are the core of safe Aider use.
Step 4: Let Aider lint and test the change
Aider automatically lints and tests your code after every change, and can fix problems your linters and test suites detect. Still run your project’s own test command, and read the output before accepting the commit. If a test fails, paste the failure back into the chat.
Step 5: Work across the whole codebase
For larger projects, Aider’s repository map helps it work across many files. You can also add images and web pages to the chat for visual context when working with a vision-capable model. Keep the same discipline: one change at a time, diff review, tests, then move on.
Pricing / Limitations
Aider itself is free open-source software under the Apache 2.0 license. There is no per-seat fee for the tool. What you pay for is the LLM behind it: API usage from providers such as Anthropic, OpenAI, or DeepSeek, billed by those providers, plus more tokens when you load large files or whole repositories into the chat. Check your provider’s pricing page for current rates; the README does not state pricing. Limitations to plan around:
- Terminal-only: there is no graphical interface. Staff who do not use the command line will not be able to use it.
- Token costs scale with context: adding many files costs more and can confuse the model. Add only what the change needs.
- Model-dependent quality: results vary by model. The README lists Claude 3.7 Sonnet, DeepSeek R1 and Chat V3, and OpenAI o1, o3-mini, and GPT-4o as working best; check the official docs and leaderboards for current guidance.
- Review is still mandatory: Aider commits automatically, which is convenient — and exactly why you must read each diff before pushing. Never push Aider’s commits to a shared branch without review.
Bottom line for SMB
Aider is one of the best-value tools for a small team that already works in git: free, terminal-native, and disciplined about commits and diffs. Install it, point it at one real file, make one small change, and review the diff — that first hour tells you whether it fits. If your team does not write code, skip it. Full details: aider.chat/docs.
FAQ
Do I need a paid API key to use Aider?
Aider itself is free, but you need access to an LLM — usually a paid API key from a provider such as Anthropic, OpenAI, or DeepSeek, or a local model. The tool does not include a model.
Which languages does Aider support?
Over 100, including Python, JavaScript, Rust, Ruby, Go, C++, PHP, HTML, and CSS, according to the README.
Can I undo a change Aider made?
Yes. Aider commits its changes to git, so you can use /undo in the chat to undo its last commit, or use standard git tools to diff, manage, and undo changes.
