Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add DamiMartinez/book-skills --skill lean-startupgit clone --depth 1 https://github.com/DamiMartinez/book-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/damimartinez/book-skills/lean-startup)<a href="https://agentmods.dev/skills/damimartinez/book-skills/lean-startup"><img src="https://agentmods.dev/badge/skills/damimartinez/book-skills/lean-startup/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/damimartinez/book-skills/lean-startup"><img src="https://agentmods.dev/badge/skills/damimartinez/book-skills/lean-startup.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00152 | $0.01027 |
| Opus 5 | $0.00076 | $0.00513 |
| Sonnet 5 | $0.00030 | $0.00205 |
| Haiku 4.5 | $0.00015 | $0.00103 |
Grade A, and why
lean-startup scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.
The Lean Startup
Apply this skill to structure plans, feature proposals, or decisions around Eric Ries's core idea: treat a new product, feature, or business idea as a series of experiments that test unproven assumptions, not a spec to be built in full.
Core concepts
Leap-of-faith assumptions — Every new idea rests on assumptions that could be wrong. The two biggest: the value hypothesis (will people actually want/use this?) and the growth hypothesis (how will this spread/scale?). Identify these explicitly before proposing a build plan.
Build-Measure-Learn loop — The core cycle. Go in reverse when planning: decide what you need to learn, figure out what metric answers that, then design the minimum thing to build to get that data. Most people plan forward (build → measure → learn) and waste effort; lean planning starts from the learning goal.
MVP (Minimum Viable Product) — Not a smaller/crappier version of the final product. It's the smallest experiment that generates validated learning about a leap-of-faith assumption, with the least effort. An MVP can be a landing page, a concierge manual process, a Wizard-of-Oz fake front-end, a single feature — whatever tests the riskiest assumption fastest. When proposing an MVP, always name which assumption it tests.
Validated learning — Progress means proof that assumptions hold (or don't), backed by data from real customer behavior — not opinions, not "we shipped X features." If a plan can't say what would count as disproof, it isn't validated learning yet.
Innovation accounting — Track progress with a small number of actionable metrics tied to the hypotheses, not vanity metrics (total signups, pageviews, cumulative totals — numbers that only go up and don't inform decisions). Prefer cohort-based, per-customer, ratio metrics that can go up or down and drive a decision.
Actionable vs. vanity metrics — A metric is actionable only if: it shows clear cause and effect, it's understandable/memorable, and it changes behavior. If a metric can't fail a test, it's vanity — call this out when a user proposes success metrics.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 42 lines · 152 tokens per session scan A 48f0a088a0bf
lean-startup is a skill published in the GitHub repository DamiMartinez/book-skills (11 stars, last pushed 1mo ago), licensed MIT. It adds 152 tokens to every session and 1,027 once invoked, about $0.0008 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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