“They wrote the book on it.”

Leanpub

The Definitive Guide to Agent Evals

by You

A real, published book on your category — ghostwritten in your voice, from just a few hours of you talking. It starts with a half-hour call.

Four sessions: three to make the book, one to record your podcast episode
Six weeks: from first session to published book — half a batch
$24,000 for MVP: or $48,000 for the PMF version (details below)

Book a half-hour call

The week after Demo Day, every deck looks the same

Your whole batch has a deck, a launch post, and roughly the same round. A launch post has a 48-hour half-life. GitHub stars mean nothing to a VP. A benchmark table dies at the next model release. All of it works on developers. None of it works in the rooms where your next round and your first big deals get decided — rooms you are not in.

“They wrote the book on agent evals” is a sentence other people say for you, in exactly those rooms. The partner who wants to lead your round has to re-sell you at the Monday partner meeting, to a partnership you never get to pitch — this is the sentence they carry in. Your champion says it to their VP to push the pilot through procurement. The candidate who Googles you before betting a career on a six-person company finds an author, not another deck. There is no such sentence for stars, benchmarks, or launch posts. A book is the only credibility signal with a stock English idiom attached.

Stripe built a publishing house to get this. You can get it in six weeks for the price of a conference booth. Start it the week after Demo Day, and it’s live while your round is still open.

Your own tribe just proved it: Principles of Building AI Agents, by Mastra’s cofounder (YC W25), is 133 pages — and it’s everywhere. (To be clear: we were not involved with that book in any way. We’re linking it here since we think it’s the perfect example of a startup using a small book tactically for big marketing benefits.) The short book has always been the form: Rework is about 27,000 words and was a bestseller; The Mom Test is 33,700 words and sits on university syllabi. Short is the point.

The definitive book on the exact problem your startup is solving is still unwritten. Once we ghostwrite it with you, you are the person who wrote the definitive book on it.

You talk. GhostAI writes. A Leanpub founder edits. You review.

You talk. One deep recorded interview — 90 to 150 minutes, booked at checkout — where you’re interviewed not just by Peter Armstrong or Len Epp, but by GhostAI too. During this first session, we interactively build out your book’s outline with you, combining human judgment and the GhostAI skills. Plus your existing public writing: launch posts, blog posts, talks, podcast appearances. Plus, provide us with any internal documentation you can share.
GhostAI writes. GhostAI is the suite of AI skills we built at Leanpub on Anthropic’s frontier model, Claude Fable 5. The skills teach Fable to write like you: it studies your recorded interview and your writing samples (public blog posts, conference talk recordings, and private samples you provide, like emails or university essays), learns your voice, and drafts book-length chapters in it — at a speed no human ghostwriter can touch. An eval harness scores every chapter for fidelity to how you actually talk.
A Leanpub founder edits. Every chapter is reviewed and edited — in conjunction with the AI editing tools we built — by one of Leanpub’s founders: either Peter Armstrong, founder of Leanpub with over two decades as a software developer and the author of multiple technical and non-technical books, or Len Epp, a former investment banker with a DPhil in English from Oxford and the host of the Leanpub Podcast. That combination is the whole point: Fable 5 ghostwriting guided by the actual creators of GhostAI, plus full human review. You get incredible quality and incredible speed, in your voice. The result is polished and professional.
You review it with us. Shortly after the interview, you get the draft of the whole book. In a second recorded session we go through it together — you react to the whole thing, go deep on the sections that matter, and just talk; that conversation feeds straight back into GhostAI. The third session is the final review: touch-ups and sign-off before we publish.

You can choose to ship with an optional colophon — “How this book was made” — disclosing the whole method: recorded conversations and your writing samples, drafted by GhostAI in your voice, measured by an eval harness, edited by a Leanpub founder, reviewed and approved by you.

What we never do is ship words you haven’t approved. Everything passes the eval harness, a founder’s edit, and your review before it publishes.

Two Versions

Pick which speed and quantity suits you.

MVP

Minimum Viable Product

A real, published book on the problem your startup is solving — ghostwritten in your voice from one deep recorded interview plus your writing samples, then refined with you across two review sessions.

$24,000USD all-in

Book a half-hour call

15,000–30,000 words, ghostwritten in your voice
Published in six weeks, in every format, print-ready
Your ebook is published on Leanpub in PDF and EPUB
Your book is published on Amazon in Kindle and paperback
250 paperback copies sent to you via Amazon, so you can give them to potential investors and prospects
Additional paperbacks whenever you need them, ordered at cost from Amazon KDP as author copies
A crawlable store page and free sample chapters — the surface answer engines read
A gated free edition that captures reader emails, with their consent
A launch interview video — a short, ~10-minute interview
A launch-timed episode of the Leanpub Podcast — typically a 30- to 60-minute interview, published on the Leanpub YouTube channel and on your book page
A feature in our weekly newsletter, which reaches 90,000 readers, and our monthly newsletter, which reaches 140,000 readers
Four sessions: one to record, one to iterate, one to review, one for the podcast interview — under eight hours all-in

PMF

Product-Market Fit

Half the time, double the print run, double the price. Everything in Minimum Viable Product, for the startup that is racing.

$48,000USD all-in

Book a half-hour call

Everything in Minimum Viable Product
Published in three weeks instead of six — half the time
500 paperback copies instead of 250, sent to you via Amazon, so you can give them to potential investors and prospects
The book is live everywhere within the three weeks; printed copies arrive on Amazon’s shipping schedule
One slot per month

For calibration: premium ghostwriting agencies charge $50,000 to $150,000 and up — and take about a year. Freelance ghostwriting floors at $0.60 a word — $11–15,000 of raw human labor for a book this length, before editing, design, or publishing.

But frankly, who cares about all that. As a startup, what you are racing against is time. That’s why we win. Against human ghostwriting of any kind, our difference is fidelity and speed: drafted from your own recorded words, in your voice, published in six weeks — or in three weeks with the PMF upgrade.

These are Leanpub books — the same store that has been publishing developer books for 15 years. We decline books we don’t believe in; everything we accept goes on the shelf next to them.

For Y Combinator Startups

The Founder Book is a cash engagement. The prices above are our standard terms — all-in, and the same for everyone.

For Y Combinator companies, we make one exception — not to the price, but to how we’re paid: we’ll accept up to half of our fee in equity, because we’d like to be long-term partners in what you’re building. Of course, you can also just pay fully in cash, if you prefer.

Here’s why: writing the definitive book on your category means spending weeks inside your thinking. Some of the companies we do that with are companies we’d rather hold a stake in than simply invoice. We take on a small number of these partnerships, and we choose them carefully.

For YC-backed startups

Minimum Viable Product

Everything in Minimum Viable Product above.

Cash

$24,000

Cash + equity

$12,000 cash

+ $12,000 in equity

Product-Market Fit

Everything in Product-Market Fit above.

Cash

$48,000

Cash + equity

$24,000 cash

+ $24,000 in equity

For this initial launch of the program, equity is accepted at face value — a dollar of equity counts as a dollar of fee.

Book a half-hour call

By accepting part of our fee in equity, we’re making a long-term investment in companies we believe have exceptional potential. Our success becomes aligned with yours.

Your effort budget, to the minute

Frankly, since you’re in an accelerator, your time is more valuable than ours. That’s why we’ve built the Founder Book process to support you and help you win.

What	Your time
The call that starts it	30 minutes
Checkout, booking all four sessions at once	15 minutes
The interview — you pitch all day; this is that	90–150 minutes
The draft review session — the whole book lands; you react, we go deep	60–90 minutes
The final review session — touch-ups and sign-off	60–90 minutes
Recording your episode of the Leanpub Podcast	90 minutes
Recording your launch interview video	30 minutes
Total	Under 8 hours

Our promise:
“You get a book you can use tactically in your fundraising and marketing, in under 8 hours of your time.”

A book normally costs its author over 300 hours of writing. Yours costs you less than 8 hours, with zero writing.

Frequently asked questions

Is it my voice?: Yes — and it’s measured, not vibes. We built AI skills so Fable learns how to write like you: GhostAI drafts only from your raw material — the interview plus your writing samples — and an eval harness scores every chapter against how you actually talk. A Leanpub founder reviews and edits before you ever see it, and in the review sessions you flag anything that doesn’t sound like you.
Do I approve everything?: Yes — but not chapter-by-chapter with a thumbs-up button. You get the whole draft after the interview, then two recorded review sessions with us: one to react to the whole book and go deep where you want, one for final touch-ups. Nothing publishes until you’ve signed off.
What if you sell this to my whole batch?: Capacity is the honest limit: a human editor gates every chapter, so we can only publish a handful of books per batch, not hundreds. Besides, we’re not that good at marketing. Finally, your book is in your voice, about your topic — another founder’s book, even in a category near yours, is a totally different book by a completely different person. The signal is your name and your thinking.
Who owns it?: You do. Copyright and royalties. The book publishes under your name — on the Leanpub store and on Amazon.
Isn’t this AI slop?: Slop is undisclosed, unaccountable generation. This is the opposite: a thorough interactive interview from GhostAI, built on deep engineering and customer feedback, an eval harness that measures every chapter, a Leanpub founder’s review of everything, your review of the whole draft, and an optional colophon disclosing the method. You build under eval constraints. So do we.

It starts with a half-hour call

Thirty minutes with either Peter Armstrong or Len Epp, founders of Leanpub. We talk through your category, the raw material you already have — talks, posts, podcast appearances — and what your table of contents could look like. If we don’t believe there’s a book in it, we will say so right on the call. We only want to do this if it helps you win.

Book a half-hour call