# define-hypothesis

Turns an assumption about user behavior into a falsifiable statement with success metrics and a validation plan, before you design any experiment.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 806 installs · ★ 763
- Author: product-on-purpose
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/product-on-purpose/pm-skills/tree/HEAD/skills/define-hypothesis/SKILL.md
- Updated: 2026-10-21
- HTML: https://affpapa.org/en/nevibecode/skills/define-hypothesis

## What it does

The skill walks the agent through six steps: state the belief as "we believe that [change] for [user] will [outcome]", name the target segment, describe the expected behavior change, pick success metrics, choose a validation approach, and list risks and assumptions. Output follows `references/TEMPLATE.md` and fills every section: hypothesis statement, background, target segment, success metrics, validation approach, risks, timeline. A finished example sits in `references/EXAMPLE.md`.

It deliberately stops short of experiment design. Variants, sample size and duration belong to `measure-experiment-design`. If the problem itself is unframed, run `define-problem-statement` first; for a discovery structure use `define-opportunity-tree`, and for the whole business model `foundation-lean-canvas`. Worth checking where you are in the process, because this skill covers framing only.

A quality checklist runs before the document is handed back: the hypothesis must be falsifiable, the success metric needs a numeric target, and pass/fail criteria have to be unambiguous.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add product-on-purpose/pm-skills --skill define-hypothesis -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/define-hypothesis/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/define-hypothesis/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add product-on-purpose/pm-skills --skill define-hypothesis -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/define-hypothesis/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add product-on-purpose/pm-skills --skill define-hypothesis -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/define-hypothesis/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install product-on-purpose/pm-skills define-hypothesis
```

2. **Manually: put the files in place**
- File: `.github/skills/define-hypothesis/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add product-on-purpose/pm-skills --skill define-hypothesis -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/product-on-purpose/pm-skills --path skills/define-hypothesis
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/define-hypothesis/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add product-on-purpose/pm-skills --skill define-hypothesis -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/product-on-purpose/pm-skills/tree/HEAD/skills/define-hypothesis/SKILL.md

## When to use it
- write a hypothesis that can be proven wrong
- attach a numeric target to the success metric
- separate what you are testing from how you test it
- get a team to agree on what success looks like
- record assumptions and risks before engineering starts

## Example prompts
- Define a hypothesis for the new onboarding funnel
- Draft a hypothesis: we believe day-one tips will lift 7-day return rate
- Fill the hypothesis template for the new-user segment

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 8cb8862bd7ce4337.

BEGIN THIRD-PARTY FILE 8cb8862bd7ce4337
```text
---
name: define-hypothesis
description: Defines a testable hypothesis with clear success metrics and a validation approach. Use when forming assumptions to test or aligning a team on what success looks like, before any experiment is designed. To design the A/B test or experiment that will validate the hypothesis, use measure-experiment-design.
license: Apache-2.0
metadata:
  phase: define
  version: "2.1.0"
  updated: 2026-06-10
  category: ideation
  frameworks: [triple-diamond, lean-startup, design-thinking]
  author: product-on-purpose
---
<!-- PM-Skills | https://github.com/product-on-purpose/pm-skills | Apache 2.0 -->
# Hypothesis

A hypothesis is a testable prediction about how a change will affect user behavior or business outcomes. It transforms assumptions into explicit statements that can be validated or invalidated through experimentation. Well-formed hypotheses prevent teams from building features based on untested beliefs and create shared understanding of what success looks like.

## When to Use

- After problem framing, before committing to a solution
- When designing experiments or A/B tests
- When team members have differing assumptions about user behavior
- Before investing significant engineering resources in a feature
- When pivoting direction and need to validate the new approach

## When NOT to Use

- You are ready to design the actual A/B test (variants, sample size, duration) -> use `measure-experiment-design`; this skill frames what to test, not how
- The problem itself is still unframed -> use `define-problem-statement` first
- You want to organize many assumptions and ideas into a discovery structure -> use `define-opportunity-tree`
- The team needs the full business-model picture, not one testable claim -> use `foundation-lean-canvas`

## Instructions

When asked to create a hypothesis, follow these steps:

1. **State the Belief**
   Articulate what you believe will happen. Use the structured format: "We believe that [action/change] for [target user] will [expected outcome]." Be specific about the intervention - vague hypotheses can't be tested.

2. **Identify the Target User**
   Define who this hypothesis applies to. A hypothesis about "users" is too broad. Specify the segment: new users in their first week, power users with 10+ sessions, churned users returning, etc.

3. **Define the Expected Outcome**
   What behavior change or result do you expect? Frame it in terms of user actions (complete onboarding, make a purchase, return within 7 days) rather than internal metrics when possible.
```
END THIRD-PARTY FILE 8cb8862bd7ce4337

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