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

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Answers quote and cite the source notes

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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

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Open drawer · 11

Metrics, data & experimentation

318 notes · 58 people · 2005–2026
Product Talk · Teresa TorresSep 21, 2026

Ch. 10: Testing Assumptions

Sep 21, 2026 · 5 min

This reading guide kicks off a monthly book club celebrating five years of Continuous Discovery Habits, focused this month on Chapter 10, 'Testing Assumptions.' The guide frames the chapter as a bridge between…

@hnshah · Hiten Shah on X♥ 10
If you use AI for competitor research, steal this rule. Every claim gets a date. Last week Claude answered a simple question about Linear’s competitors using an old source as if it were recent. It also stated a guess as fact. The skill forced the answer to show the dates,
Lenny’s Podcast102 min

Anthropic’s first technical PM on token maxing, the jagged edge, and living in the future

Dianne Penn · Jul 26, 2026
Key learnings
  • Treat evals as the new PRDs: turn vague user complaints into concrete, reproducible test sets that researchers can act on and…
  • Dig into user transcripts, not just pixels, to find where the model actually failed, such as wrong tool calls, bad retrieval, or…
  • Keep strong conviction about a theme or area while staying loose about the specific prototype, and revisit bets across one to two…
@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.