Business idea stress test

Challenge a business idea on customer, problem, model and economics, then get a verdict and the cheapest tests to prove or kill it.

Change note: Initial version

Prompt

Act as a skeptical but constructive investor evaluating my business idea. Your job is to find the weak points before I invest time or money.

Idea: {{idea}}
Target customer: {{customer}}
How we will make money: {{model}}
Why we think we can win: {{edge}}
Resources I have (time, money, skills): {{resources}}

Evaluate in this order:
1. **Restatement**: the idea in one sentence and the core bet it relies on.
2. **Scorecard** (1 to 5 with a one-line reason): problem severity, customer clarity, solution advantage, willingness to pay, ease of reaching customers, unit economics, defensibility, founder fit.
3. **Fatal flaws**: anything that would kill the idea, if it exists. If none, say so.
4. **Riskiest assumptions**: the 5 beliefs that must be true, ranked by how risky and how important they are.
5. **Cheapest tests**: for each of the top 3 assumptions, a test I can run in under 2 weeks for under {{test_budget}}, with a clear pass/fail threshold.
6. **Back-of-envelope economics**: price, cost, margin, customers needed to earn a living. Show the arithmetic and state the assumptions.
7. **Verdict**: Go, Pivot, or Stop, with the three reasons that matter, and one way to reshape the idea if you suggest a pivot.

Be blunt but specific. Praise only what is actually strong.

Variables

• {{idea}}The idealongrequired

  Default: A subscription service that delivers curated spare-parts kits to independent bike shops

• {{customer}}Target customertextrequired

  Default: independent bicycle shops with 1 to 3 staff

• {{model}}How we make moneytextrequired

  Default: monthly subscription of $120 plus a 10% mark-up on parts

• {{edge}}Why we can wintextrequired

  Default: I ran a bike shop for 8 years and know which parts sell out

• {{resources}}Resourcestextrequired

  Default: $15k savings, 15 hours per week, no software skills

• {{test_budget}}Test budgetselectrequired

  Options: $100, $500, $1,000

  Default: $500

Example output

**Core bet:** small bike shops will pay a monthly fee to stop running out of fast-moving parts.

| Criterion | Score | Reason |
|---|---|---|
| Problem severity | 3 | Stockouts hurt, but shops already have distributor accounts |
| Customer clarity | 4 | Clear segment, easy to list |
| Willingness to pay | 2 | Subscription plus mark-up on thin-margin parts is unproven |
| Unit economics | 2 | Shipping and inventory risk eat the 10% |
| Founder fit | 5 | Direct industry experience |

**Fatal flaw:** none confirmed, but margin risk is serious.

**Riskiest assumptions:** shops lack reliable restocking; they will pay above distributor price; you can predict demand per shop; shipping is cheap enough; owners will switch suppliers.

**Cheapest tests (under $500)**
1. Call 25 shops: do at least 8 describe stockouts costing over $500 a month?
2. Offer a manual kit to 5 shops at the proposed price: 2 of 5 should pay.
3. Quote distributor lead times and compare.

**Economics:** $120 + 10% on about $400 parts = $160 revenue; if parts cost $360 and shipping $15, gross profit is about $25 per month. To earn $4k a month needs about 160 shops.

**Verdict: Pivot.** Charge for the service (inventory forecasting) rather than marking up parts.

Notes

Scoring the idea against explicit criteria and demanding pass/fail thresholds for each test turns opinion into a plan. Run the cheapest test before building anything.