Aider Tutorial 2026: Git-Native AI Pair Programming

This Aider tutorial gets you from install to a safe daily workflow: install Aider with aider-install, start it in your git repository with your own model API key, add the files to change, and describe the change. Aider edits the files and commits each change separately, so you review with /diff and roll back any edit with /undo.

Commands and flags checked October 2026 against Aider's install guide, git integration docs and in-chat command list.

Most AI coding tools treat git as something you deal with afterwards. Aider puts it at the centre: each AI edit is a commit with a descriptive message, which turns "the AI changed something" into a reviewable, revertible history. That single design choice is why many developers keep Aider alongside heavier agents. For how it fits with Claude Code, Cursor and the rest, see our AI coding tools guide.

Aider tutorial: what you will have at the end

• Aider installed in its own environment, connected to a model of your choice.
• A commit-per-change workflow with review and undo built in.
• A simple way to estimate what your sessions cost.

Prerequisites

Step 1: install Aider and connect a model

Aider's install page shows the same pattern for other providers, such as OpenAI and DeepSeek models. If you are on the Claude API, our guide to getting a Claude API key covers creating and limiting one.

The Aider git workflow, step by step

Here is the daily loop that makes Aider safe to use on real code. It relies on behaviour Aider documents on its git page.

1. Start clean. Aider takes care with files that already have uncommitted changes: by default it commits your preexisting changes first, with a descriptive message, so your edits stay separate from its edits. Starting from a clean tree keeps history easy to read.
2. Add only the files the change needs. Use /add for files to edit and /read-only for reference files. Aider also builds a repo map, a compact summary of your repository's files and key symbols, and sends the most relevant parts with each request, so it knows the wider codebase without you adding everything.
3. Ask for one focused change. "Add input validation to the signup handler and a test for it" works better than a list of five unrelated tasks.
4. Review with /diff. It shows every file change since your last message.
5. Keep or /undo. /undo undoes and discards the last change. Because every change is its own commit, undo is exact.
6. Run tests with /test. It runs your command and adds the output to the chat when it fails, so Aider can fix what broke.

If you prefer to review before anything is committed, start Aider with --no-auto-commits and use /commit yourself. Aider also marks its commits: by default it appends "(aider)" to the git author or committer name, and flags such as --attribute-co-authored-by change how that attribution appears.

Habits that make Aider sessions go well

The tool is simple; the results depend on how you drive it. A few habits separate productive sessions from frustrating ones.

• Write requests like tickets. Say what should change, where, and how you will know it worked. "In auth.ts, reject passwords under 12 characters and add a test in auth.test.ts" gives Aider everything it needs.
• Ask before you change. In an unfamiliar repository, spend the first few minutes in /ask mode. Understanding where things live saves several failed edits later.
• Keep commits small. One request, one change, one commit. Small commits make /undo precise and make code review by teammates realistic.
• Let tests close the loop. Run /test after each change. When it fails, Aider sees the output and can fix the problem in the next commit.
• Squash before you merge. Aider's commit-per-change history is great while working. Before a pull request, squash or rewrite the branch into commits your team wants to read.

None of this is specific to Aider, but its git-first design rewards it more than most tools. The history it leaves behind is also a record of how a feature was built, which helps when you come back to the code months later.

The commands you will use daily

Two modes are worth learning early. /ask answers questions about the code without editing, which is ideal for understanding an unfamiliar repo before you change it. /architect splits work between two models, one that plans the change and one that writes the edits.

Bring-your-own-key cost math

Aider is open source, so the software is free; you pay your model provider per token. That changes how to think about cost. A subscription tool charges a flat monthly price; Aider charges whatever your sessions use.

A simple way to estimate: each request sends the added files, the relevant part of the repo map and the chat history, then receives the edit. Use /tokens to see how large your context is. As an illustrative calculation, not a measurement, at a published rate of USD 2 per million input tokens and USD 10 per million output tokens (Claude Sonnet 5.5 on Anthropic's API pricing, checked October 2026), a session of 40 requests averaging 30,000 input tokens and 2,000 output tokens each would use 1.2 million input and 80,000 output tokens, roughly USD 2.40 plus USD 0.80. Your numbers will differ, so measure a real week with /tokens and your provider's usage page before comparing.

The cost levers are the same as with any API workload: fewer files in context, shorter chats (use /clear between unrelated tasks), and a cheaper model for simple edits. If you are building products with these tools, our AI SaaS Builder program covers the full build and launch workflow.

Aider vs OpenCode

OpenCode is another open-source terminal coding agent. Its documentation says it supports 75+ LLM providers and local models, offers /undo and /redo that revert the latest message and the work after it, and includes a plan agent that analyses code without making changes (checked October 2026 on opencode.ai). The practical difference is philosophy: Aider builds its safety net from git commits, while OpenCode manages reverts inside its own session and leans further toward autonomous agents. If git history is how you think about change, Aider fits naturally; if you want an agent that runs larger tasks with less steering, OpenCode or Claude Code may suit better. Our Claude Code install guide covers that route.

Troubleshooting

• Edits land in the wrong file. The right file was not added. /add it and drop unrelated ones.
• Costs climbing. Check /tokens; drop files and /clear old chat before new tasks.
• Commits mixed with your own work. Start sessions from a clean tree, or use --no-dirty-commits if you want Aider to leave your uncommitted files alone.
• Aider does not see a new file. Files created outside the session are not in the chat until you /add them, so add new files explicitly before asking Aider to edit them.
• Edits fail to apply. Try a stronger model, or architect mode so planning and editing are split.

Aider tutorial: FAQ