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Risk · Explore, Choose, Review

Assumption mapping

Separates what you know from what you are betting on, then sorts the bets by how much damage a wrong one would do. Cheap, fast, and skipped almost universally.

The printable canvas and the handoff into Claude Code are part of a paid plan. See what a plan includes. It needs the Claude desktop app on this machine, and your team and the prompt library already installed in that project — we cannot see your disk, so open it there.

Stage
02 Explore, 03 Choose, 05 Review
Works at
All levels
Maturity
Any
Time
An hour

What it is

A method for surfacing everything a plan takes on faith, then sorting by importance and evidence so effort goes to the assumptions that both matter and are unverified. Its value is disproportionate to the hour it takes.

The assumption inventory
Everything the plan requires to be true — about customers, competitors, cost, capability, timing and capital. Extracted line by line rather than recalled.
Importance
Whether the plan survives this being false. Only load-bearing assumptions deserve further attention.
Evidence
How well established it is: measured, inferred, heard once, or assumed. Most teams find rather more in the last two categories than expected.
The critical quadrant
Important and unevidenced. This is the output — usually four or five assumptions carrying the entire plan.
Test design
The cheapest, fastest way to check each critical assumption, and what result would falsify it.
The mistake people makeThere is almost no argument against doing this: it takes an hour, needs no data, and the top-right quadrant reliably contains something nobody had noticed. It is skipped because it delays the plan by an afternoon and makes the sponsor uncomfortable.
What it’s forYou want to separate what you know from what you are betting on.
What it’s not forNever, really. It is cheap, and it is the tool most often skipped.

How you run it

  1. Extract the assumptions from the planRead it line by line asking what has to be true for this sentence to hold. Most plans contain thirty or forty; the load-bearing ones number about five.
  2. Rate each on importanceIf this were false, would the plan still work? Anything that survives being wrong is not load-bearing and can be set aside.
  3. Rate each on evidenceHow much do we actually know? Distinguish measured, inferred, heard once, and assumed.
  4. Plot the two axesImportant and unevidenced is the top-right quadrant, and that is the entire output. Everything else is context.
  5. Design the cheapest test for eachFor each top-right assumption, what is the fastest and cheapest way to find out? Usually far cheaper than the cost of being wrong.

The prompt

Two ways to run it

Run this tool in your own Claude

The short prompt starts your partner against the library on your disk. The long one carries everything with it and needs nothing installed.

🔒 Prompt locked

Everything above is free — what this tool is, what it is for, what it is not for, and how to run it as a workshop. Three tool prompts a month are free with an account; beyond three, and for the printable canvas, it is the paid part.

See plans — from £19 a month

Your playbook

It lands in the earliest stage this tool suits. Move it on the Playbook page.

You’ll need

  • A plan, proposal or strategy in written form
  • People who worked on it and at least one who did not
  • Willingness to label things as unknown

You’ll end up with

  • Every material assumption listed
  • Each placed by importance and by evidence
  • A test plan for the important and unevidenced ones

Runs well with

Acquisition screen and synergy thesisAdjacency mapAfter action reviewAI opportunity map