Aider

What Aider does

Aider is a terminal-based AI pair programmer. You start a chat session pointed at your git repo, add files to the conversation, and tell Aider what you want changed. Aider talks to the LLM, applies the changes to your files using a reliable diff format, and automatically commits the changes with a descriptive commit message.

Unlike browser-based tools, Aider runs entirely locally in your terminal and integrates deeply with git. You always see what's happening: the LLM response, the diff being applied, and the commit being made. This makes Aider transparent and auditable — critical for production codebases.

Aider consistently ranks at or near the top of the SWE-bench leaderboard (a benchmark measuring autonomous code editing performance), often outperforming commercial tools like Copilot Workspace.

Getting started

pip install aider-chat

# Configure your API key
export ANTHROPIC_API_KEY=sk-ant-...
# or
export OPENAI_API_KEY=sk-...

# Start Aider in your project directory
cd my-project
aider --model claude-3-5-sonnet-20241022

# Basic usage
aider  # uses default model (claude-3-5-sonnet or gpt-4o)
aider --model gpt-4o  # specify model
aider --model ollama/llama3.1  # use local Ollama model
aider --no-auto-commits  # review changes before committing

──────────────────────────────────────────────────────
Aider v0.50.0, model: claude-3-5-sonnet-20241022
Git repo: .git with 47 files
Repo-map: using 1024 tokens, auto refresh
────────────────────────────────────────────────────────────────
>

The /add workflow

Aider's core workflow is adding files to the chat context, then making requests. Files in the chat give the LLM read access; files added with /add give write access (Aider will modify these files).

> /add src/api/routes.py src/models/user.py

Added src/api/routes.py to the chat.
Added src/models/user.py to the chat.

> Add a /users/me endpoint that returns the current authenticated user's profile as JSON

src/api/routes.py
  + @router.get("/users/me")
  + async def get_current_user(current_user: User = Depends(get_current_user)):
  +     return current_user.to_dict()

src/models/user.py
  + def to_dict(self):
  +     return {"id": self.id, "email": self.email, "name": self.name}

Apply changes? (y/n) y
[main 3a7f8b2] feat: add /users/me endpoint returning current user profile

> /run pytest tests/test_routes.py

Architect + Editor mode

Aider's Architect mode uses a stronger model for reasoning and planning, and a faster/cheaper model for actually making the code edits. This gives you the reasoning quality of a frontier model at a fraction of the cost.

# Architect with claude-3-5-sonnet, editor with haiku (cheap)
aider --architect --model claude-3-5-sonnet-20241022       --editor-model claude-3-haiku-20240307

# Or use opus for architect, sonnet for editor
aider --architect --model claude-3-opus-20240229       --editor-model claude-3-5-sonnet-20241022

The architect model reads the full context and produces a detailed plan. The editor model takes the plan and implements the specific file changes. Because the editor's job is simpler (just apply a described change), a cheaper model performs nearly as well — typically 80–90% of the quality at 30% of the cost.

Git integration

Aider is deeply integrated with git. By default, every successful change is committed automatically with a message generated by the LLM describing what was changed and why.

# Aider respects .gitignore automatically
# Useful flags:
aider --no-auto-commits     # don't commit, just make changes
aider --dirty-commits       # commit even if repo has uncommitted changes
aider --dry-run             # show changes but don't apply them

# Undo the last Aider commit
aider --undo

# Common workflow: start on a feature branch
git checkout -b feature/my-feature
aider --model claude-3-5-sonnet-20241022
# make changes, review the auto-commits, squash before merging
git rebase -i main  # squash Aider's fine-grained commits into one

The auto-commit feature means you always have a clean rollback point. If Aider makes a bad change, just git revert the commit.

Model configuration

# Best models for Aider (benchmark performance order):
aider --model claude-3-5-sonnet-20241022  # top performer on SWE-bench
aider --model o1-mini                      # strong reasoning tasks
aider --model gpt-4o                       # reliable all-rounder

# Cost-optimised:
aider --model claude-3-haiku-20240307      # fast, cheap, good for simple tasks
aider --model gpt-4o-mini

# Local models (privacy, no API cost):
aider --model ollama/llama3.1:70b
aider --model ollama/qwen2.5-coder:32b    # best local coding model

# .aider.conf.yml — persistent configuration
model: claude-3-5-sonnet-20241022
auto-commits: true
dark-mode: true

Gotchas

Repo map context: Aider builds a "repo map" — a compressed summary of all files in your project — and includes it in every prompt. For large repos (1000+ files), this can consume significant context. Use --map-tokens 0 to disable it if context is too full.

Large file additions: Adding a 5,000-line file to the chat uses most of the context window. Prefer adding only the relevant files, or use /read (read-only) instead of /add (writeable) for reference files you don't want Aider to edit.

LLM costs: With claude-3-5-sonnet at $3/1M input tokens, a complex multi-file task can cost $0.10–$0.50 depending on file sizes. For ongoing development, the Architect+Editor pattern significantly reduces costs.

Merge conflicts: If you edit a file manually while it's also in the Aider chat, you may get merge conflicts when Aider tries to apply its diff. Pause manual editing of chat-tracked files while Aider is working.