Before you build
Find the riskiest assumption in your startup idea before you build it
Crux turns your idea into a ranked assumption map, then gives you practical experiments to test demand before you waste weeks building the wrong thing.
Built by We Scale Startups, using the same assumption-testing process we use with early-stage AI and B2B SaaS founders.
What you get, from one real idea
Paste an idea in. This comes out.
“Route-level flight reviews by flight number — when several flights cost the same, travellers can't tell which one is actually better.”
Typed in 2 minutes. No pitch deck.
Travellers care enough about route-level flight reviews to search for them before booking.
Importance 5/5 × uncertainty 5/5 — ranked #1 of 8 assumptions. If this is false, nothing downstream matters.
Launch pages for specific routes ("BA vs easyJet, London → Berlin"), drive a small amount of search and community traffic, and measure clicks and email captures. Crux deploys the test page and drafts the ad + outreach copy.
50 page visits, 10 email signups, 3 qualitative replies within 7 days.
Build, narrow, pivot, or drop — based on evidence, not enthusiasm.
Ideas do not die from bad code. They die from untested guesses.
Most founders don't need more features. They need to know what must be true for the idea to work — and which assumption to test first.
Building becomes procrastination
Writing code feels productive, but it delays the uncomfortable question: does anyone actually want this?
Generic AI gives generic validation
A chatbot can list risks, but it won't reliably turn your idea into a ranked testing plan with pass bars.
Founders test the wrong thing
Most early tests validate opinions, not behaviour. The real risk is usually demand, urgency, buyer, or channel.
From idea to experiments in minutes
No pitch deck, research doc, or product spec needed. Just the idea, in plain English.
Share your idea
What it is, who it's for, what you already believe or fear. Messy is fine — Crux handles messy.
⏱ 2 minutesGet your assumption map
Crux breaks the idea into hidden assumptions and ranks them by impact, uncertainty, and testability. #1 is your crux.
⏱ ~60 secondsLaunch the right experiments
Practical tests with pass bars — landing pages deployed with one click, plus outreach copy, survey questions, and ad angles.
🚀 Live the same dayWhat you get for every idea
Optimised for one outcome: the fastest possible evidence on whether to build, pivot, or drop.
The crux, named
The single assumption that makes or breaks the idea — with the reasoning shown. Validate it and everything downstream gets cheaper; invalidate it and you've saved six months.
Assumptions, ranked
Importance × uncertainty across desirability, viability and feasibility. Test from the top.
Experiments, designed
Falsifiable hypothesis, one metric, a numeric pass bar — smoke pages, ad tests, outbound tests, concierge runs.
Pages & copy, generated
Test pages live with one click, plus outbound messages, survey questions, and ad copy — conversion tracking built in.
Human review in the pilot
Every pilot assumption map is reviewed by We Scale Startups before you spend money on traffic — AI leverage with operator judgement on whether the experiment will actually settle the question.
Why not just ChatGPT?
ChatGPT can give you a list of risks. Crux gives you a decision system — one workflow that extracts the hidden assumptions, ranks the riskiest, designs practical experiments, and helps you decide whether to build, test, pivot, or drop.
Where it sits
Just build it
3–6 months
- Feels productive, tests nothing
- Sunk cost compounds
- Market verdict arrives last
Accelerator / course
£500–5k + months
- Frameworks, not execution
- Cohort pace, not your pace
- Experiments still on you
Crux
Free map · paid pilot
- Ranked assumption map in minutes
- Experiments with pass bars
- Smoke pages deployed for you
Generic AI chat
£20/mo
- Tells you it's a great idea
- No metrics, no pass bar
- Nothing goes live
Test 5 ideas before you build them
For founders, creators, and operators sitting on too many ideas. Submit up to 5 ideas and for each one you get:
- The riskiest assumption, named
- A ranked assumption map
- Practical validation experiments with pass bars
- Landing page, survey, or outreach copy where useful
- Human review from We Scale Startups
- A clear build, test, pivot, or drop recommendation
Or start self-serve: get your assumption map free →
Questions idea people ask
Won't ChatGPT do this for free?
Ask ChatGPT about your idea and you'll get encouragement. Crux gives you falsifiable assumptions with scores, a ranked order to test them in, experiments with numeric pass bars — and then actually deploys the smoke-test pages. The difference is evidence, not opinions.
What does "automatically implemented" mean?
Smoke-test experiments go live as real hosted landing pages — headline, benefit bullets, signup capture, view and conversion tracking — the moment you click Launch. Ad and outbound experiments come with copy ready to paste; you keep control of budgets and sending.
Do I need traffic for the experiments to work?
Yes — a smoke page with no visitors proves nothing. Each experiment includes the ad copy and outbound messages to drive traffic. £50–100 of ads or 30 targeted messages is usually enough to get a signal against the pass bar.
What if an assumption gets invalidated?
That's a win. An invalidated crux for £50 beats a failed launch after six months. The map shows what to test next — or tells you to pivot the idea while it's still cheap to do so.
Who reviews the experiments?
Daniel Johnson and We Scale Startups — hands-on GTM work with founder-led B2B startups. In the pilot, every assumption map and experiment design gets operator review before you spend time or money testing the wrong thing.
Is this for SaaS only?
No. The method works for any idea with a customer and a price: SaaS, services, marketplaces, content businesses, physical products. The experiments adapt — smoke pages and outreach for B2B, ads and waitlists for consumer.
What happens after I apply?
You'll get an email within a couple of days. If there's a fit, you submit your ideas and get your first assumption map the same week. The pilot is free while we refine the process — in exchange we want honest feedback.