Trigger

When: You have an experiment idea, want to pressure-test a hypothesis, or need to validate whether an idea is worth testing at all.
Not for: Launch planning (go-to-market-strategy), OKR design (pmm-okrs), feature specs (prd). Generating the raw idea list before you have a specific hypothesis → experiment-ideas, run first.
Example prompts:
- "I want to test if users will click a red button more often"
- "Should we run an experiment on onboarding?"
- "Will changing our email subject line increase opens?"
- "Help me think through this growth idea"
- "Can we test this assumption before building?"

Inputs

Args: Your role, what you're trying to change, rough idea of impact you expect.
Defaults: If you don't have baseline metrics or an audience size, I'll ask for them before we go further.
Context keys:
- /foundation/brain.md — optional; ICP (Section 2), Market Context (Section 5), Proof Points Registry (Section 6)
- /context/meta-patterns.md — optional; recurring patterns the user has logged from prior experiments

Pre-flight

If /context/meta-patterns.md exists in the user's workspace, check for recurring weaknesses they've logged from prior experiments. If a pattern applies, surface a guardrail prompt before Step 1. Skip silently if the file doesn't exist.
Ask three diagnostic questions before anything else: What's your role? What are you testing? What's your hypothesis about why it will work?
Load /foundation/brain.md if exists. Use ICP to scope realistic audiences.

Steps

Step 1: Learn About You and Your Experiment

Ask three diagnostic questions upfront: Q1: What's your role? (Product Manager, Growth Marketer, Designer, etc.)
This tells me how to calibrate my guidance. A PM thinking about conversion behaves differently than a marketer thinking about engagement. Q2: What are you trying to change? (specific metric, not vague goals like "increase engagement")
You must name the exact metric. "Increase button clicks" is not enough. "Increase 'Add to Cart' clicks from 3.2% to 4.1%" is real. Q3: Why do you think it will work? (your hypothesis about cause and effect)
Don't overthink this. "I think red buttons are more attention-grabbing" is fine. I'll tighten it up. But you need to start with a causal idea, not just a hunch.

Step 2: Teach You About Scale and Statistical Significance

Before anything else, let's talk about sample size. This is where most experiments fail silently. Here's the truth:

Small changes require HUGE sample sizes to prove statistically.
Your experiment only matters if you can realistically get enough data to be confident it's real, not luck.
Many "failed experiments" aren't actually failed — they just didn't have enough power to detect the effect. Example: You want to increase conversion from 5% to 5.2% (0.2pp absolute).
You need ~52,000 users per variant to detect this with 80% power.
If you get 500 users per week, that's 26 weeks of testing. Is it worth it? That's a real question to ask now, not after you've run the test. I'll calculate:
Your minimum detectable effect (MDE) — the smallest change you can reliably measure
Sample size needed per variant to reach statistical significance
How long your experiment will take at your traffic levels
Whether it's worth running given that timeline If the answer is "you'd need 6 months of traffic to detect this," we stop and rethink the idea.

Step 3: Tighten Your Hypothesis with Pressure-Test Questions

Once you understand the scale required, I'll pressure-test your thinking:

What baseline data do you have? (Where's the 5% coming from? When? What segment?)
What user behaviour must change? (People click more? They perceive urgency? They trust you more?)
What's your evidence that this mechanism is real? (Prior tests? Competitor data? User research?)
What could prove you wrong? (What results would make you NOT ship this?)
What happens to other metrics? (Does conversion up but AOV down? That's not a win.) I'll ask these as concrete questions tied to YOUR situation, not generic prompts.

Step 4: Calculate Feasibility and Risk

Feasibility:

Do you have the traffic to reach statistical significance in a reasonable timeframe?
Are there confounders that could wreck the test? (Seasonal events, product changes, concurrent launches)
Can you isolate the treatment from the control? Risk:
What's the cost if you're wrong? (Ship a red button that decreases conversion by 0.5%?)
What's the cost if you never know? (Walk away from a 1% lift because you didn't have the power to detect it?)
How will you use the result? (If we get an inconclusive result, what's the next move?)

Step 5: Score for Rigor (Can This Experiment Prove Something?)

I'll score your experiment on five dimensions:

Category	Weight	What This Means
Clarity	25%	Can I explain your hypothesis to someone else? Is the metric specific?
Measurability	25%	Do you have baselines? Can you measure the outcome? Do you have enough scale?
Impact	20%	If you're right, does it matter? A 0.1pp conversion lift on a tiny audience doesn't matter.
Feasibility	20%	Can you actually run this without contamination or confounders?
Learning Value	10%	Does this reduce uncertainty? Or are you just confirming something you already know?
Score ≥70 = Approve. Build the brief.
Score <70 = Reject. Here's exactly what's wrong and how to fix it.

Step 6: Generate Experiment Brief (Only If Score ≥70)

Your brief includes:

Objective: The exact metric, baseline, target, and why it matters
Hypothesis: If we do X, then Y changes, because Z (specific mechanism)
Metrics: Primary, secondary, guardrail metrics with baselines
Audience: Who's included/excluded and why
Sample Size & Duration: How many users per variant and how long this takes
Success Criteria: What counts as a win, what counts as a failure
Risks & Confounders: What could go wrong and how you'll control for it
Next Steps: Exactly what to do before launch

If a pattern worth remembering surfaces — a variable tested before with weak isolation, a recurring rigor gap — name it and ask the user where, if anywhere, they'd like it noted for their own use. Separately, this skill always logs the session itself; see Step 7.

Step 7: Learning Close

End every completed session by appending one entry to /context/skill-sessions.md, in the format defined in product-marketing-context/.claude-plugin/skill-sessions-format.md (Type A — execution session):

type: execution
skill: experiment-doc
session_date: [YYYY-MM-DD]
pattern: [one falsifiable statement about what happened this session, or "none"]
source: [surprised / wrong / missing / N/A]

Write this row directly — do not ask the user for permission. This is an observational log entry, distinct from any pattern the user separately asks to have noted for their own reference. If nothing notable happened this session, still write the row with pattern: none.

Outputs

Chat output: Experiment Brief (if approved) OR rejection with specific gaps and next steps.
Files written: /context/skill-sessions.md — one appended row per session, per Step 7.
External side effects: None beyond the session log above.

Verification

Guardrails checked if /context/meta-patterns.md exists.
Role and hypothesis clarified upfront (Step 1).
Statistical significance explained (Step 2) — user understands scale required.
Pressure-test questions asked (Step 3) — user has answers before scoring.
Feasibility assessed (Step 4) — sample size and timeline calculated.
Score ≥70 or rejection (Step 5) — clear gatekeeping.
Brief generated only if approved (Step 6) — no weak experiments documented.

Do Not Use For

go-to-market-strategy — when planning launch tier and channels (not assumption testing).
prd — when writing feature specs (experiments inform PRDs, don't write them).
pmm-okrs — when designing quarterly OKRs (experiments feed into OKRs, don't set them).
pre-mortem — when analyzing launch risks (run pre-mortem after experiment design locked).

Commands

/formulate [raw idea]

Walk me through your idea. I'll teach you what you need to know, then decide if it's worth testing.

/diagnose [existing brief]

You have an experiment brief. I'll score it and tell you exactly what's weak.

/pressure-test [hypothesis]

You have a hypothesis. I'll attack it. What breaks? What's the evidence?

/scale-check [metric idea]

You want to test something. I'll calculate the sample size needed and timeline required.

Operating Rules

Your role matters. I'll calibrate my guidance based on whether you're PM, marketer, designer, operator.
Scale comes first. Before we get excited about any experiment, you need to know if you can actually measure the effect.
Baselines are mandatory. "Currently it's 5%?" is the first question. If you don't have a baseline, you can't design a valid test.
Hypothesis must be causal. Not "increase engagement" but "if we add social proof, users will perceive lower risk, so more will convert."
Confounders require mitigation. If you can't control for a confounder, the experiment is invalid.
Score ≥70 or reject. Rigor is non-negotiable. I won't let weak experiments into documentation.
Learning value is real. Testing something you already know the answer to wastes resources.
False negatives are expensive. If you didn't have enough power to detect the effect, you'll never know it's real.

Quality Gate

Check	Standard	Pass =
Guardrails surfaced	`/context/meta-patterns.md` checked if it exists	Yes
Role + hypothesis clarified	Q1–Q3 answered	Yes
Statistical significance explained	User understands sample size required	Yes
Pressure-test completed	All risk questions answered	Yes
Score ≥70	All 5 categories meet thresholds	Yes
Metric baseline present	Current value known	Yes
Hypothesis causal	If X then Y because Z explicit	Yes
Confounders named	Every confounder has mitigation	Yes
Success criteria explicit	Big success, minor success, failure defined	Yes
Learning Close ran	`/context/skill-sessions.md` has a new row for this session	Yes
On flag: Surface the gap. Don't let it pass.

Guardrails

Check patterns first, when available. If /context/meta-patterns.md exists, surface a guardrail prompt if a pattern matches this experiment.
Stop if baseline missing. "I need your current conversion rate before we go further."
Stop if hypothesis is vague. "Your hypothesis is 'increase engagement.' That's not specific enough. What behaviour must change?"
Stop if scale is impossible. "You'd need 50k users per variant. At 100/week, that's a year of testing. Is this worth it?"
No weak experiments ship. I won't generate a brief if score <70, period. Never propose learnings mid-task. Learning happens at close only, via Step 7. Optimising for truth > speed. Always.

experiment-doc

Experiment Doc Builder