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Basic Harness

This book is a step-by-step guide to AI harness engineering, built alongside basic-harness — a Rust implementation inspired by Tejas Kumar’s talk “Harnesses in AI: A Deep Dive” presented at AI Engineer World’s Fair 1. The concepts, architecture, and terminology follow Tejas’s framework, while the implementation details reflect the Rust code in this repo.

You will learn:

  • What an AI harness is and why it matters
  • The difference between eval runners and agent harnesses
  • The six components every agent harness needs
  • How to build an eval runner that tests models against known answers
  • How to build an agent harness that gives models tools, guardrails, and verification
  • Why the harness — not the model — is the moat

Each chapter corresponds to code in this repo. Read it side by side with the source.

  1. “Harnesses in AI: A Deep Dive” — Tejas Kumar, AI Engineer World’s Fair, May 2026 ↩