The Leanpub 60 Day 100% Happiness Guarantee
Within 60 days of purchase you can get a 100% refund on any Leanpub purchase, in two clicks.
See full terms...
Architect Your Agent's Harness
The Architecture Techniques Behind AI Agents That Don't Hallucinate or Waste Tokens
This book is 100% completeLast updated on 2026-06-15
You have built an AI agent that works beautifully in a demo, then falls apart the moment real users arrive: it invents answers, burns through tokens, and freezes on slow tools. The problem was never your prompt. This book shows you the real fix, layer by layer, and turns "I hope my agent works" into "I can prove it does."
With Membership
Free!
$7.98
You pay
Author earns
PDF
About
About the Book
An AI agent is code, not a prompt. The harness, the engineering layer around the model (tools, control loop, retrieval, memory, validation, guardrails), is what decides whether your agent hallucinates or wastes tokens. You do not fix those failures by editing the system prompt; you architect them into the harness.
This book takes one travel booking agent that demos well and breaks in production, and rebuilds its harness one technique at a time: grounded retrieval, semantic tool selection, guardrails in code, multi-agent validation, the memory pointer pattern, async handles, debounce hooks, evaluation, and observability. Every technique ships as runnable code with measured before-and-after numbers. Each chapter also shows you exactly what to tell an AI coding assistant to build that layer for you.
Feedback
Author
About the Author
Elizabeth Fuentes
Elizabeth Fuentes Leone is a data scientist who builds and teaches reliable, cost-efficient AI agents. She turns frontier AI research into named, reproducible techniques and ships them as open-source code that anyone can run, study, and deploy. She publishes hands-on technical tutorials, and her work on stopping agent hallucinations and curbing wasted tokens is used by developers across the community, independent of any single platform or vendor.
Get the free sample chapters
Click the buttons to get the free sample in PDF or EPUB, or read the sample online here
Earn $8 on a $10 Purchase, and $16 on a $20 Purchase
We pay 80% royalties on purchases of $7.99 or more, and 80% royalties minus a 50 cent flat fee on purchases between $0.99 and $7.98. You earn $8 on a $10 sale, and $16 on a $20 sale. So, if we sell 5000 non-refunded copies of your book for $20, you'll earn $80,000.
(Yes, some authors have already earned much more than that on Leanpub.)
In fact, authors have earned over $15 million writing, publishing and selling on Leanpub.
Learn more about writing on Leanpub
Free Updates. DRM Free.
If you buy a Leanpub book, you get free updates for as long as the author updates the book! Many authors use Leanpub to publish their books in-progress, while they are writing them. All readers get free updates, regardless of when they bought the book or how much they paid (including free).
Most Leanpub books are available in PDF (for computers) and EPUB (for phones, tablets and Kindle). The formats that a book includes are shown at the top right corner of this page.
Finally, Leanpub books don't have any DRM copy-protection nonsense, so you can easily read them on any supported device.
Learn more about Leanpub's ebook formats and where to read them
Write and Publish on Leanpub
You can use Leanpub to easily write, publish and sell in-progress and completed ebooks and online courses!
Leanpub is a powerful platform for serious authors, combining a simple, elegant writing and publishing workflow with a store focused on selling in-progress ebooks.
Leanpub is a magical typewriter for authors: just write in plain text, and to publish your ebook, just click a button. (Or, if you are producing your ebook your own way, you can even upload your own PDF and/or EPUB files and then publish with one click!) It really is that easy.