Aider

What it is

Aider is a command-line pair-programming tool. You describe a change in plain English, and Aider edits the right files, shows you a clean diff, and (optionally) auto-commits with a meaningful message. It treats your git repo as the source of truth and excels at "make this change, then commit it" workflows.

Best for

• Pair programming from the terminal
• Migrate APIs or libraries across a repo
• Generate clean, reviewable commits for every step

Quick start

1. Install: `pip install aider-chat` (Python 3.8+ with pipx recommended).
2. Set your API key: `export OPENAI_API_KEY=sk-...` (or `ANTHROPIC_API_KEY`, `GEMINI_API_KEY`, etc.).
3. From inside a git repo, run: `aider hello.js` — Aider starts a chat session with hello.js added to context.
4. Describe the change in plain English; Aider will show a diff and (by default) auto-commit each successful change.
5. Use `/add <file>` and `/drop <file>` mid-session to refile files; `/undo` rolls back the last commit; `/diff` shows what changed.

Sample input / output

$ aider hello.js
> write a JavaScript function `sumArray(nums)` that returns the sum, with a docstring and a JSDoc return type.
  Then write 3 Vitest tests covering empty arrays, mixed numbers, and decimals.

hello.js (new):
  /**
   * Sums an array of numbers.
   * @param {number[]} nums
   * @returns {number} sum
   */
  export function sumArray(nums) { return nums.reduce((a, b) => a + b, 0); }

hello.test.js (new): 3 tests, all passing.
2 new commits:
  a1b2c3d feat(hello): add sumArray with JSDoc
  d4e5f6a test(hello): vitest suite for sumArray

Benchmarks

Pricing

Free; bring your own API keys

Underlying models