Rebuilding the 'pi' Coding Agent in 600 Lines of TypeScript

What it does This project teaches you how a coding agent ticks by rebuilding the core of pi in roughly 600 lines of TypeScript. The resulting nano-pi handles file reads, code edits, and shell commands through an OpenAI-compatible API, but the deliverable is comprehension, not a framework.

The interesting bit The tutorial lives on a custom site where the article and source code share the stage: scroll through the prose and a side editor progressively writes itself, while a trace viewer lets you step through the agent loop with breakpoints—no local debugger required.

Key highlights

• ~600 lines of TypeScript, stripped of production engineering noise
• Reproduces the pi agent’s data flow with “intuitive” hand-built components
• Website syncs scrolling text with live code generation in an embedded editor
• Trace viewer uses pre-generated static data, so the tutorial runs offline
• Needs Node.js 22 and an OpenAI-compatible key to run the agent locally

Caveats

• The hosted trace is static; you’ll need local setup plus an API key to see live agent behavior
• Explicitly billed as an article, not a library—expect pedagogy, not plug-and-play automation

Verdict Perfect if you want to understand agent loops by watching one grow from zero. Skip it if you need a mature coding assistant for your day job.