Assumptions Map

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About This Tool

An assumption is anything your plan needs to be true but that you have not yet confirmed. Most plans carry far more assumptions than people realize, and the dangerous ones are usually the quiet, load-bearing assumptions nobody thought to question. The Assumptions Map gives those assumptions a home. Instead of arguing about opinions, you make each assumption explicit, judge how much rests on it and how much evidence supports it, and let that decide where to spend your attention — testing the risky few rather than worrying about everything at once.

How to Use

  1. Add the assumptions behind your decision, or pull in ones you already captured in the other Decisions tools. Use the guided prompts if you are not sure what you are assuming.
  2. Rate each assumption by importance and by how much evidence you have, then read the map. The assumptions in the Test-first zone are your priorities.
  3. Design a quick test for a risky assumption, record what you learn, and set a signpost so you get an early warning if it starts to break. Update its status as the picture becomes clearer.

Methodology

The map plots each assumption on two axes: importance (how much your decision depends on it) and evidence (how much support you actually have). High-importance, low-evidence assumptions are the riskiest and belong at the top of your testing list — what lean practitioners call leap-of-faith assumptions. To surface assumptions, the tool offers structured prompts drawn from established practice: a Key Assumptions Check, a leap-of-faith prompt, a checklist of common assumption areas, and stakeholder questions. To act on them, you can design a quick test, record what you learn, set a signpost (an early-warning sign that an assumption is breaking), and update each assumption's status over time.

Sources: A Tradecraft Primer (US Gov, 2009) · Yang, Liang & Avgeriou (2018)

Understanding Your Results

Each assumption lands in one of four zones. Test first (important, little evidence) is where your real risk lives — design a test before you commit. Monitor (important, well-evidenced) assumptions are load-bearing but currently supported; set a signpost so you notice if that changes. Park (low importance, little evidence) assumptions can wait. Note (low importance, well-evidenced) assumptions are safe to record and move on. The goal is not to eliminate every assumption — that is impossible — but to make sure no important one goes untested by accident.

Practical Examples

A founder planning a paid app lists the assumption "people will pay $10/month for this." It is highly important and has almost no evidence, so it lands in Test first. Instead of building the whole app, she runs a small pre-sale to test it — turning a leap of faith into real evidence before committing months of work. A team launching in a new region assumes "local regulations allow our model." Important and only partly evidenced, it lands near the Test-first edge. They set a signpost — a check with a local advisor before launch — so a wrong assumption cannot surprise them late.

Tips for mapping assumptions

Write each assumption as a clear statement you could be wrong about — "new customers will pay within 30 days," not "cash flow." Vague assumptions cannot be tested. Rate evidence honestly. A strong opinion is not evidence; a single anecdote is weak evidence. Most early assumptions belong on the low-evidence side, and that is fine. Do not try to test everything. Pick the one or two assumptions that are both important and weakly supported, and test those first. Revisit the map regularly. Evidence changes, and an assumption that was safe last quarter can quietly become risky.

All calculations are performed locally in your browser. No data is sent to any server.

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Frequently Asked Questions
What counts as an assumption?
An assumption is anything your decision needs to be true but that you have not confirmed. "Customers will renew," "we can hire the team in time," and "the supplier can scale" are all assumptions. The most dangerous ones are usually invisible — the load-bearing beliefs nobody thought to question — which is exactly why writing them down matters.
How do I decide importance versus evidence?
Importance is how much your decision depends on the assumption: if it turned out false, how much would have to change? Evidence is how much real support you have right now — data, tests, or experience, not opinion or hope. Rating both honestly is the whole point: it moves you from "everything feels risky" to a clear view of which few assumptions actually are.
Which assumptions should I test first?
The ones that are both important and weakly evidenced — the Test-first zone of the map. These are sometimes called leap-of-faith assumptions: your plan depends on them, yet you are mostly taking them on faith. Testing one of these early, while it is still cheap to be wrong, is far more valuable than polishing things you are already confident about.
How do I actually "test" an assumption?
Design the smallest experiment that would give you real evidence, decide in advance what result would count as pass or fail, run it, and record what you learned. A pre-sale, a landing page, a few customer interviews, or a quick technical spike are all valid tests. The aim is to replace a guess with evidence before you commit, not to build the whole thing first.
What is a signpost?
A signpost is an observable early-warning sign that an assumption is starting to break — a metric crossing a line, a customer behavior, a regulatory change. For important assumptions you cannot fully test up front, a signpost tells you when to re-examine the decision, so a shift in reality does not catch you by surprise later.
How does this connect to the other Decisions tools?
Assumptions you surface elsewhere — for example during a pre-mortem in Decide, or while exploring options in Navigate — flow into a shared pool, and the Assumptions Map is where you manage them. It becomes the single place to see every assumption across your decisions, prioritize them, and track which ones you have actually tested.
Is my data private?
Yes. Everything you enter is saved only in your browser, on your device. Nothing is sent to a server. You can export your assumptions at any time for backup, and delete everything whenever you choose.