Minimal Coding Agent

A coding agent in under 400 lines of Python. It connects to any LLM through OpenRouter and can read, write, search, and execute code autonomously.

How it works

You ↔ agent.py (chat loop) ↔ OpenRouter API ↔ Any LLM
              ↓
      tools.py (5 tools + dispatch)
              ↓
      sandbox.py (subprocess with timeout)

The agent runs a simple loop: send your message to the LLM, execute any tool calls it requests, feed results back, repeat until it responds with text.

Tools

Tool	What it does
read_file	Read a file's contents
write_file	Create or overwrite a file
run_command	Execute a shell command (with timeout)
list_directory	List files and folders
search_files	Search for text patterns across files

Setup

pip install -r requirements.txt
copy .env.example .env   # then add your OpenRouter API key

Usage

python agent.py

Coding Agent (model: minimax/minimax-m2.5)
Type /quit to exit, Ctrl+C to interrupt.

You: Create a fizzbuzz.py that takes a number from the command line, then run it with 20
  🔧 write_file({"path": "fizzbuzz.py", "content": "..."})
  🔧 run_command({"command": "python fizzbuzz.py 20"})

Agent: Done! Here's the output:
1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz, ...

Tests

python -m pytest tests/ -v

43 tests across two suites — no API key needed:

• test_easy.py (17 tests) — happy-path validation for every tool
• test_medium.py (26 tests) — edge cases, error handling, multi-tool workflows

Files

agent.py      — Chat loop + OpenRouter API calls (147 lines)
tools.py      — Tool schemas, implementations, dispatch (196 lines)
sandbox.py    — Subprocess wrapper with timeout (44 lines)
prompts.py    — System prompt (20 lines)

Configuration

Set these in your .env file:

Variable	Default	Description
OPENROUTER_API_KEY	(required)	Your OpenRouter API key
OPENROUTER_MODEL	minimax/minimax-m2.5	Any model on OpenRouter