Working notes from product people

Ask the people who’ve done it.

A free, searchable library of 1,799 of the best product-management essays, podcast episodes and posts, from Lenny Rachitsky, Marty Cagan, Teresa Torres and seven others, that answers your questions with citations.

For PMs, founders and anyone building products

Q:
Answers quote and cite the source notes

Unofficial · not affiliated with any author · every note links to the original

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Answers come from ten product leaders’ essays, podcasts and posts, not the open web.

Every claim is cited

Each point carries a numbered citation that links to the note and to the original essay or episode.

No outside knowledge

Ask writes only from the library, and says plainly when the library doesn’t cover your question.

Where to start

01 · Ask a questionGet a cited answer in seconds.

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02 · Learn a topicRead what the best people say.

14 topics, from strategy to pricing to AI, and 33 common questions already answered.

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01 — Topics · the card catalogueBrowse by topic

Postfree essay or newsletter postPaidsubscriber post, summary onlyPodcastepisode with key learningsXpost on XHover a tag for the publication

3 more drawersBrowse all 14 topics →
Open drawer · 11

Metrics, data & experimentation

318 notes · 58 people · 2005–2026
Lenny’s Newsletter · Free post♥ 225

What is good retention?

Jun 9, 2020 · 12 min

“Hello, and welcome to the free monthly editionof my weekly newsletter. I’m Lenny, and each week I tackle reader questions about product, growth, working with humans, and anything else that’s stressing you out at the office. Q: What do you consider GOOD and GREAT retention? “Great retention is the scalable way to grow a product. It’s the best indicator of product-market fit, it is the most important factor in a user’s lifetime value…”

Lenny’s Newsletter · Free post♥ 1,022

How Duolingo reignited user growth

Feb 28, 2023 · 21 min

Jorge Mazal, former CPO of Duolingo, recounts how the company reversed a slide in daily active user growth and eventually grew DAU about 4.5x over four years. The journey began with failed attempts: a…

@ttorres · Teresa Torres on X♥ 97
"The only way to know if our AI products and workflows are any good is with evals." 💡 If you're using AI to write PRDs, analyze customer feedback, or build customer-facing AI products, you need to understand evals. This guide breaks down what evals actually are and why product teams should be…
Lenny’s Podcast97 min

The ultimate guide to AEO: How to get ChatGPT to recommend your product

Ethan Smith · Sep 14, 2025
Key learnings
  • Everything that works in traditional SEO also works for AEO, so start with landing pages targeting high-volume keywords before…
  • In LLM answers you win by being mentioned across many citations, not by ranking first, so pursue multiple third-party mentions…
  • Early-stage companies can win in AEO quickly, since a single citation from a Reddit thread, YouTube video, or blog can get you…
Lenny’s Podcast96 min

The ultimate guide to A/B testing

Ronny Kohavi · Jul 27, 2023
Key learnings
  • Test every code change, since even small bug fixes or tiny UI tweaks can have surprising, large impact on key metrics.
  • Expect most ideas to fail: roughly two-thirds to over 90% of experiments in his experience did not move the target metric, so…
  • Allocate a portion of experiments to high-risk, high-reward bets, accepting that about 80% will fail, while keeping most work…
@ttorres · Teresa Torres on X♥ 9
💭 "I wish I could click on this card and be like, 'Clean this up.'" When a customer pointed out a flat, unstructured branch in her AI-generated opportunity solution tree, it sparked a three-week journey to fix the problem at its source. Here's what you'll learn from this article: How one customer…

02 — FrameworksModels, annotated.

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03 — PeopleWho wrote the notes.

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04 — QuestionsAnswered from the notes.

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Where notes come from

NewsletterLenny’s Newsletter110 free posts, with a longer excerpt.
Subscriber postsSummary only233 paid posts: our summary, at most two short quotes, and a link.
PodcastLenny’s Podcast323 episodes, each with 5–8 key learnings and timestamps.
EssaysSVPG · The Beautiful Mess499 essays from Marty Cagan and John Cutler.
Substack & blogsShreyas · Julie · Jason · Hiten577 essays and posts from independent writers.
XPosts on product66 posts, filtered for product relevance.