Exploring the frontiers of language models, agents, and software design.

A collection of notes, essays, and technical deep dives by Ivan Leo.

Previously built general agents for knowledge work at Manus (acq by Meta). Embarking on a new adventure soon.

Featured Series

Building an Agent

A comprehensive series on building AI coding agents from scratch, covering everything from basic tool integration to advanced features like agentic search and subagents.

Start Reading

1 PartsIn Progress

LLMs From Scratch

Working through Stanford's CS336 and documenting what I learn at each step — from tokenization to training.

Start Reading

Latest Articles

Pydantic to Regex: Compiling JSON Schemas for Structured Outputs

Build a recursive JSON Schema-to-regex compiler from first principles

Feb 2, 2026·Structured Outputs From Scratch

Know when to let the model cook

Taste is all that matters.

Jan 18, 2026

How I Broke Into AI Without a Roadmap

The messy, fast-changing path that took me from front-end engineering to LLMs.

Jan 12, 2026

Reversing Chinese Poetry

Creating our first RL Pipeline with Verifiers

Jan 2, 2026·Reinforcement Learning From Scratch

Three Lessons I've Learned at Manus

Lessons learnt from going from zero to $100M ARR in 8 months

Dec 22, 2025

Implementing BPE

Building a Byte-Pair Encoding tokenizer from scratch

Nov 30, 2025·LLMs From Scratch

Spinning Up RL

Getting started with reinforcement learning

Nov 9, 2025·Reinforcement Learning From Scratch

Agentic Search

Models can't do much without the right context, agentic search does just that

Oct 11, 2025·Building an Agent