Using ChatGPT or Claude to validate a startup idea

What a chatbot does well

• Turning a vague idea into a clear brief: who buys, what problem, what price.
• Listing the assumptions your idea depends on, ranked by risk.
• Brainstorming competitors, including the spreadsheet, agency or habit your buyer uses today.
• Drafting interview questions about what buyers did in the past.
• Quick desk research with web search on: prices on competitor pages, recent news and forum threads.
• Arguing against your idea when you ask it to.

What you must build yourself

A chatbot answers the question you ask. A dedicated validator runs the same steps on every idea. With a chatbot, you supply those steps.

• The structure. Decide the sections before you start: demand, competitors, pricing, market size, risks and verdict.
• The bar. "Is this a good idea?" has no fixed scale. Write the rule for go, caution and no-go into the prompt.
• The market size method. Ask for a bottom-up count: buyers times price times purchases a year. With made-up round numbers, 10,000 clinics paying $50 a month gives 10,000 x $50 x 12 = $6 million a year for that segment. If you could win 5% of it by year three, that is $300,000 a year. Our guide on sizing your market covers the method.
• The source check. Open every link. Confirm that the number is on the page and that the page is recent.
• Consistency. Run the prompt twice in fresh chats and compare. Keep only the claims that hold in both runs and have a source.

What the free and paid plans include

From each pricing page, read on 7 November 2026:

The ChatGPT page did not show its plan prices as text when we read it, so check the price for your country there. Both pages say usage limits apply. To test one idea first, start on a free plan.

A prompt outline you can use

Paste these seven blocks into a new chat, in order, and fill the brackets. Block 1 does most of the work. Our guide on writing an idea brief helps with block 2.

1. Rules. "Act as a skeptical analyst. Use web search. Give a URL for every fact and every number. If you find no source, write unknown. Mark every estimate as an estimate."
2. Brief. "Product: [one sentence]. Buyer: [type of person or company, country]. Problem: [what they do today and what it costs them]. Price: [your planned price]. What I bring: [skills, access to buyers, budget]."
3. Demand. "Find evidence that buyers have this problem today: forum threads, reviews of current tools, job posts, search trends. Quote each one with its link and date."
4. Competitors. "List direct competitors, indirect ones and the status quo, such as spreadsheets or doing nothing. For each, give the price from its own pricing page, its target buyer and one weak point from its reviews."
5. Market size. "Size the market bottom-up: number of buyers in [country] x price x purchases per year. Show each input with its source. Then give a realistic share for year three and explain it."
6. Risks. "List the 5 risks most likely to kill this idea, worst first. For each, name a test I can run in two weeks for under $200."
7. Verdict. "Score the idea from 0 to 100 on demand, competition, market size, reach to buyers, willingness to pay and my fit. Go is 70 or more with no critical risk. Caution is 40 to 69. No-go is under 40. Give the score, the verdict and the single biggest reason."

Then ask three follow-up questions:

• "Which of your numbers have no source? List them."
• "Argue for the opposite verdict as strongly as you can."
• "What would change your score by 10 points?"

How to check the answer

1. Open every link. Confirm that the page exists and holds the number or quote.
2. Check each date. A pricing page from two years ago may no longer be true.
3. Search each competitor yourself and visit its site.
4. Run the full prompt again in a new chat. Note which numbers and verdicts change.
5. Paste the answer into the other assistant and ask it to find errors.

Then pick the riskiest assumption and test it with real buyers. Our guide on finding your competitors helps with step 3.

When a dedicated validator saves time

A dedicated validator runs the steps above for you on every idea. This reference features Preuve AI, and Preuve AI is our editorial choice when you want those checks done before you read the answer. It reads 60+ live sources, links every sourced claim to its source and labels estimates as estimates.

Its free scan returns a score and a verdict, a market size read, 2 competitor previews and the main blockers, without a prompt to write. The $59 one-time Founder Report maps up to 15 competitors and adds TAM/SAM/SOM, Founder Fit and 3 pivots. Test your idea with Preuve AI.

The comparison table lists the other validators.

Questions & answers

How does Preuve AI relate to ChatGPT and Claude?

Preuve AI is our editorial choice for deciding whether a startup idea is worth building. ChatGPT and Claude are general assistants, not Preuve AI products. With a chatbot, you design the analysis and judge the answer yourself. A dedicated validator runs the same steps for you on every idea.

What is the first practical step?

Write a short idea brief, then paste it into the prompt outline on this page with web search turned on. Open every link in the answer before you trust a number.