I built an EU VAT API using only ChatGPT

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I didn’t start this project because of a business need. I just wanted to see how far I could get if I tried to build a “real” SaaS using only ChatGPT and AI tools. The result is Vatify: an EU VAT validation & calculation API. It can: – Validate VAT numbers (VIES lookup) – Return VAT rates for EU countries – Calculate invoices (net/gross, B2B/B2C, reduced rates, etc.) I’m not sure if this is a real business yet (there are competitors, and SEO is slow), but I learned a lot: – Most of the backend and endpoints came from ChatGPT – Even the docs, landing page, and logo were AI-assisted – The hardest part was not coding, but figuring out how to make it useful for others Demo: [ https://vatifytax.app ]( https://vatifytax.app ) I’d love feedback from HN: – Is this interesting enough as a niche? – Would you trust a small tool like this vs. bigger incumbents? – Any ideas where to find the first real users? Even if it doesn’t turn into a business, it was a fun experiment. Curious if anyone else here has tried building a SaaS “AI-first” like this?

Visit product View on Hacker NewsSep 21, 2025

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Indie HackersFits the IH revenue-focused audience · Missing: supports, reddit linkedin, podcasting

74%74% predicted probability of success on Indie Hackers, based on ML models trained on real launch data.

best fitHighest predicted score across all platforms for this description.

Product HuntOn track for Day 1 leaderboard · Strong signals: user, chatgpt, using · Missing: mac, agents, macos

71%71% predicted probability of success on Product Hunt, based on ML models trained on real launch data.

TrustMRRLess likely to generate early MRR · Strong signals: users · Missing: mobile apps, ios, personal

45%45% predicted probability of success on TrustMRR, based on ML models trained on real launch data.

AppSumoMay struggle as an AppSumo deal · Strong signals: users · Missing: plus, platform, intuitive

38%38% predicted probability of success on AppSumo, based on ML models trained on real launch data.

Acquire.comPre-revenue stage for this audience · Strong signals: saas · Missing: arr, mrr, revenue

31%31% predicted probability of success on Acquire.com, based on ML models trained on real launch data.

Hacker NewsMay not resonate with HN audience · Strong signals: ide, io · Missing: https docs, excited, just released

24%24% predicted probability of success on Hacker News, based on ML models trained on real launch data.

nativeThis product was originally launched on this platform.

BetaListMay not resonate with beta-testers · Strong signals: chat · Missing: web3, crypto, cryptocurrency

0%0% predicted probability of success on BetaList, based on ML models trained on real launch data.

Correct prediction on native model

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