cs2381 Notes: 09-29 Vibe Coding with Aider

Today, we’re going to build Missile Command

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For simplicity, we’ll start with the starter code for Lab 05, largely because that lab already opens a graphics window.

Aider Install and Setup

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• Need Python and Git
  • On Debian family linux:
    • sudo apt install python-is-python3 pipx git build-essential
    • pipx install aider-chat
  • On Windows / Mac:
    • https://python.org/
    • https://git-scm.com/
    • https://aider.chat/
• Get an OpenRouter API key
  • https://openrouter.ai/
  • Give them $10 for credits; this both allows the use of premium models, and marks your account as paid which may make free models cheaper.

Aider config file (~/.aider.conf.yml):

api-key: OPENROUTER=sk-or-v1-[...]
model: openrouter/qwen/qwen3-coder
edit-format: diff
weak-model: openrouter/qwen/qwen-turbo

• Create new git repo:
  • git init .
• In the repo directory, run aider (aider)

Then we can start chatting with our AI dev buddy.

Key Ideas: Context and Messages

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Aider works by sending a chat message with some extra data about our project, including a portion of the existing source code.

• /read-only path/to/file.java # Aider sends a copy to the LLM, but can’t modify this file.
• /add path/to/file.java # Aider sends a copy to the LLM, which can chose to modify this file.
• /ask Question… # Aider should send a message and modify nothing.
• Instructions # Aider should make a change to the code.

So let’s write Missile Command…