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SaladDay

SaladDay/pi-from-scratch

A step-by-step tutorial that builds a minimal TypeScript coding agent from scratch, able to read files, edit code and run commands.

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What is it?

PI from Scratch is a hands-on tutorial that rebuilds the core ideas of the pi coding agent in about 600 lines of TypeScript, called nano-pi. It follows pi's data flow and implements each component only as far as needed to understand it, leaving out production engineering details.

The project is delivered as a readable article paired with source code. On the companion website, the code in the editor is filled in progressively as you read, and a trace feature lets you step through execution line by line with breakpoints. The agent runs against any OpenAI-compatible API, configured through environment variables for the API key, model name and base URL.

Online traces are pre-generated static data, so browsing the site does not make model requests. Running nano-pi locally requires Node.js 22 or later.

Key features

  • 01Builds a coding agent that reads files, edits code and runs shell commands.
  • 02Follows pi's data flow, keeping only the core design ideas.
  • 03Pairs article text with source code that fills in progressively in the editor.
  • 04Includes a trace viewer for stepping through code execution with breakpoints.
  • 05Works with any OpenAI-compatible API via environment variables.

Use cases

  • Learning how a coding agent loop, tool calling and file editing work internally.
  • Building your own small agent as a foundation before studying pi in depth.
  • Teaching agent architecture in a workshop or course setting.

Quick start

  1. 1

    Install Node.js 22 or newer and get an OpenAI-compatible API key

  2. 2

    Install dependencies

    npm install
  3. 3

    Set your API key

    export NANOPI_API_KEY=your-api-key
  4. 4

    Start the project

    npm run dev

Things to know

  • Requires an OpenAI-compatible API key to run the agent.

Featured in Repolode Weekly

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Open-source AI agent frameworks & appsAI coding assistants & agents

Topics

#ai-agent#coding-agent#llm#tool-calling#typescript#tutorial#agent-loop#llm-agent#pi#pi-agent

FAQ

What is pi-from-scratch?
A step-by-step tutorial that builds a minimal TypeScript coding agent from scratch, able to read files, edit code and run commands. PI from Scratch is a hands-on tutorial that rebuilds the core ideas of the pi coding agent in about 600 lines of TypeScript, called nano-pi. It follows pi's data flow and implements each component only as far as needed to understand it, leaving out production engineering details.
Is pi-from-scratch free to use? What license does it have?
pi-from-scratch is open source under the MIT license. Check the license terms before using it in commercial products.
Is pi-from-scratch still maintained?
Actively maintained. The last commit to pi-from-scratch was on Oct 24, 2026.
What can I use pi-from-scratch for?
Learning how a coding agent loop, tool calling and file editing work internally. Building your own small agent as a foundation before studying pi in depth. Teaching agent architecture in a workshop or course setting.
How do I install pi-from-scratch?
Install Node.js 22 or newer and get an OpenAI-compatible API key Install dependencies: npm install Set your API key: export NANOPI_API_KEY=your-api-key Start the project: npm run dev
Where can I get pi-from-scratch?
The source code and installation instructions are on GitHub: https://github.com/SaladDay/pi-from-scratch

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