letscode-cli 0.1.0

A from-scratch coding agent — bring your own OpenRouter API key

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Building Claude Code from scratch — a minimal coding agent you own and understand.

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What is this?

letscode is a coding agent built from first principles. It replicates the core loop of tools like Claude Code:

• You describe a coding task in plain English
• The agent calls tools (read files, list directories, edit files) to get the job done
• It keeps looping — reading, reasoning, editing — until the task is complete

The entire agent fits in a single file. No magic, no abstractions you didn't write yourself.

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Features

• Model-agnostic — works with any model on OpenRouter: Claude, GPT-4o, Gemini, Llama, Mistral, DeepSeek, and more
• Free tier support — defaults to meta-llama/llama-3.3-70b-instruct:free (no cost)
• Three core tools built in: read files, list directories, edit files
• Text-protocol tool-calling — no vendor lock-in; the LLM emits tool calls as plain text
• Full conversation history — the agent remembers context across turns

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Quickstart

1. Clone the repo

git clone https://github.com/your-username/letscode.git
cd letscode

2. Set up your API key

Copy the example config and add your OpenRouter key:

cp .env.example .env

Edit .env:

OPENROUTER_API_KEY=sk-or-your-key-here

That's all you need. The default model is free — no credit card required.

3. Run it

uv run letscode

Or, if you prefer pip:

pip install -e .
letscode

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Bring Your Own API Key (BYOK)

letscode routes all LLM calls through OpenRouter, which gives you a single API key that works with dozens of models.

Get a free key:

1. Sign up at openrouter.ai
2. Go to openrouter.ai/keys → create a key
3. Paste it into your .env file as OPENROUTER_API_KEY

Choose your model by setting OPENROUTER_MODEL in .env:

# Free models (no cost)
OPENROUTER_MODEL=meta-llama/llama-3.3-70b-instruct:free
OPENROUTER_MODEL=google/gemma-3-27b-it:free
OPENROUTER_MODEL=deepseek/deepseek-r1:free

# Frontier models (paid, best quality)
OPENROUTER_MODEL=anthropic/claude-sonnet-4
OPENROUTER_MODEL=openai/gpt-4o
OPENROUTER_MODEL=google/gemini-2.5-pro

Browse all available models at openrouter.ai/models.

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How it works

The agent runs a simple loop:

User input
    └─▶ LLM reasons about the task
            └─▶ Emits a tool call  (e.g. tool: read_file({"filename": "app.py"}))
                    └─▶ Agent executes the tool
                            └─▶ Result fed back to LLM
                                    └─▶ Repeat until done

Available tools:

Tool	What it does
read_file(filename)	Read the full content of a file
list_files(path)	List files and directories at a path
edit_file(path, old_str, new_str)	Replace text in a file, or create a new file

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Project structure

src/letscode/
  agent.py       # the entire agent: tools, prompt, parser, loop
pyproject.toml   # package config
.env.example     # config template — copy to .env

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Requirements

• Python 3.12+
• uv (recommended) or pip
• A free OpenRouter API key