Build-Measure-Learn
The loop is the unit of startup work. Not the sprint, not the release, not the
quarter: the loop — hypothesis, smallest experiment, measurement, learning, repeat.
This skill plans, tracks, and retro-dicts loops. Its entire job is making sure no loop
starts with "build."
The Loop
The loop is drawn learn-first: decide what you need to learn, design the smallest
experiment that teaches it, define how the result will be measured, build the minimum
to run the experiment, measure against the pre-declared threshold, write down what is
now believed and why, and let the learning pick the next loop.
A loop that starts with build produces a product in search of a question. That is the
failure mode this skill exists to prevent.
Modes
Plan mode (default — user brings an idea, feature, or initiative)
- Force the hypothesis first: "We believe [action] will cause [measurable outcome]
because [mechanism]." If the user cannot state one, help extract it — and if none
exists, say so: the initiative is a bet, not an experiment, and gets flagged.
- Identify what must be learned before anything is built, and pick the smallest
experiment that produces it. Often the answer is a smoke test (smoke-test-launcher)
or an MVP (mvp-type-selector), not a build.
- Define the measure BEFORE the build: metric, baseline, threshold, date. "We'll
figure out how to measure it later" is blocked — later never comes.
- Copy
templates/loop-card.md, fill every bracket, and set the loop's timebox.
Loops have deadlines; open-ended loops become projects with better branding.
Track mode (loops are running)
- For each open loop, report only three things: what was built (one line), what the
measurement says, and whether the threshold was met.
- Flag stalled loops — built but unmeasured, measured but undecided, decided but
unwritten. Each stall type has a different owner and the same cost: learning that
evaporates.
- A loop that outlives its timebox twice is closed as failed. Zombie loops consume
the team's attention budget.
Retro mode (loop completed or killed)
- Read
references/loop-failures.md for the failure taxonomy.
- Answer the four retro questions: What did we believe? What did we measure? What
actually happened? What do we now believe?
- Classify the outcome: LEARNED (threshold question answered either way — a failed
threshold is a successful loop), INCONCLUSIVE (measurement failed, not the
hypothesis — the loop gets re-run with fixed instrumentation), or WASTED (no
learning either way — name what made it wasteful; it is usually a skipped Plan-mode
step).
- The next loop is proposed from the learning, never from the backlog's old position.
Hard Rules
- Learn before build, always. The first artifact of any loop is the hypothesis.
- The measure is defined before the build, or the loop does not start.
- A loop ends in a written, falsifiable learning. Unwritten learnings are opinions
that will be re-litigated.
- Failed thresholds are successful loops. Killing a direction cheaply is the loop
working as designed.
- Smallest learnable unit, not smallest shippable product — learning defines the
size, not the roadmap.
Output Shape (Retro mode)
Loop: [name] · Outcome: [LEARNED / INCONCLUSIVE / WASTED]
Believed: [hypothesis] · Measured: [metric vs threshold]
Happened: [result] · Now believe: [one falsifiable sentence]
Next loop: [one line]
Keep output in the user's language. Never close a loop without the "now believe"
sentence.
1---2name: build-measure-learn3description: Run any product initiative through the build-measure-learn loop: define the learning first, pick the smallest experiment that produces it, decide how it will be measured before anything is built, and end every loop with a written learning. Use when planning features or experiments, when a team builds for months without learning checkpoints, when turning a roadmap item into an experiment, or when the user says build measure learn, BML loop, validated learning, smallest experiment, or plan the next loop. Not for execution management, sprint ceremonies, or initiatives with no falsifiable hypothesis at all.4---56# Build-Measure-Learn78The loop is the unit of startup work. Not the sprint, not the release, not the9quarter: the loop — hypothesis, smallest experiment, measurement, learning, repeat.10This skill plans, tracks, and retro-dicts loops. Its entire job is making sure no loop11starts with "build."1213## The Loop1415The loop is drawn learn-first: decide what you need to learn, design the smallest16experiment that teaches it, define how the result will be measured, build the minimum17to run the experiment, measure against the pre-declared threshold, write down what is18now believed and why, and let the learning pick the next loop.1920A loop that starts with build produces a product in search of a question. That is the21failure mode this skill exists to prevent.2223## Modes2425### Plan mode (default — user brings an idea, feature, or initiative)26271. Force the hypothesis first: "We believe [action] will cause [measurable outcome]28 because [mechanism]." If the user cannot state one, help extract it — and if none29 exists, say so: the initiative is a bet, not an experiment, and gets flagged.302. Identify what must be learned before anything is built, and pick the smallest31 experiment that produces it. Often the answer is a smoke test (smoke-test-launcher)32 or an MVP (mvp-type-selector), not a build.333. Define the measure BEFORE the build: metric, baseline, threshold, date. "We'll34 figure out how to measure it later" is blocked — later never comes.354. Copy `templates/loop-card.md`, fill every bracket, and set the loop's timebox.36 Loops have deadlines; open-ended loops become projects with better branding.3738### Track mode (loops are running)39401. For each open loop, report only three things: what was built (one line), what the41 measurement says, and whether the threshold was met.422. Flag stalled loops — built but unmeasured, measured but undecided, decided but43 unwritten. Each stall type has a different owner and the same cost: learning that44 evaporates.453. A loop that outlives its timebox twice is closed as failed. Zombie loops consume46 the team's attention budget.4748### Retro mode (loop completed or killed)49501. Read `references/loop-failures.md` for the failure taxonomy.512. Answer the four retro questions: What did we believe? What did we measure? What52 actually happened? What do we now believe?533. Classify the outcome: LEARNED (threshold question answered either way — a failed54 threshold is a successful loop), INCONCLUSIVE (measurement failed, not the55 hypothesis — the loop gets re-run with fixed instrumentation), or WASTED (no56 learning either way — name what made it wasteful; it is usually a skipped Plan-mode57 step).584. The next loop is proposed from the learning, never from the backlog's old position.5960## Hard Rules6162- Learn before build, always. The first artifact of any loop is the hypothesis.63- The measure is defined before the build, or the loop does not start.64- A loop ends in a written, falsifiable learning. Unwritten learnings are opinions65 that will be re-litigated.66- Failed thresholds are successful loops. Killing a direction cheaply is the loop67 working as designed.68- Smallest learnable unit, not smallest shippable product — learning defines the69 size, not the roadmap.7071## Output Shape (Retro mode)7273```74Loop: [name] · Outcome: [LEARNED / INCONCLUSIVE / WASTED]75Believed: [hypothesis] · Measured: [metric vs threshold]76Happened: [result] · Now believe: [one falsifiable sentence]77Next loop: [one line]78```7980Keep output in the user's language. Never close a loop without the "now believe"81sentence.
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