# I Built 120+ Free Online Tools. Here Are 10 Mistakes I'd Never Make Again. > Source: > Published: 2026-07-28 15:28:04+00:00 Four months ago I decided to build a simple utility website. The original plan was maybe 15–20 tools. Instead, I somehow ended up shipping 120+ tools covering PDFs, images, developers, students, finance, AI utilities, and a lot of niche calculators. Looking back, I made almost every mistake a solo developer can make. Hopefully this saves someone else a few months. **1. Stop waiting for the "perfect launch" ** Huge mistake. Nobody cares how many features you have. People care whether you solve their problem. If I started again, I'd launch after 10–20 tools and let users decide what to build next. **2. Boring tools get used more than clever ones ** Instead, the most used ones were things like: Simple wins. People search for solutions, not engineering. **3. Niche tools are an SEO superpower ** Almost nobody builds things like: The competition is almost zero. Those pages have become some of my favourites because they solve real problems. **4. Browser APIs are incredibly underrated ** Compression. Image editing. QR generation. JSON formatting. Regex testing. UUID generation. Password generation. CSV editing. All of these can happen directly inside the browser. That means: **5. Docker can save you from cold starts ** My AI background remover worked perfectly locally. Production? Every first request timed out. The reason: The U2Net model (used by rembg) downloaded on first request. Around 170 MB. The fix? Download the model during the Docker build instead. One tiny change. Massive improvement. **6. Users hate unnecessary accounts ** No email. No registration. No "Create an account to continue." People just use the tool and leave. That's exactly what most utility websites should encourage. **7. Performance matters more than animations ** Users never mentioned them. They did notice: Speed is a feature. **8. Mobile users deserve first-class treatment ** If your utility only works nicely on desktop... You've already lost a huge percentage of users. Every tool I build now starts with mobile in mind. **9. Build things you personally need ** Open it on your desktop. Scan a QR code. Start typing on your phone. The text appears instantly. No login. No app. No emailing yourself. It wasn't built because someone requested it. It solved a problem I had every week. Those are often the best products. **10. Marketing is part of building ** It doesn't. If nobody knows your project exists... It doesn't matter how clean your architecture is. Building is comfortable. Marketing is uncomfortable. Unfortunately, both are required. **Where the project is today** The project has grown into DukoTools, a collection of 120+ free online tools. Everything is free. No signup. Many tools work entirely in the browser, and the site can even be installed as a Progressive Web App for offline use. I'm now focusing on improving the existing tools based on real user feedback instead of endlessly adding new ones. If you have a favourite online tool that doesn't exist—or one that could be significantly better—I'd genuinely love to hear about it. Building is fun. Building things people actually use is even better.