I Built 31 Developer Tools Into a Single 133 KB HTML File — No Dependencies, No Backend

As a developer, I regularly find myself searching for small online utilities. Format some JSON. Decode a JWT. Test a regex. Generate a UUID. Convert a timestamp. Format an SQL query. Calculate a CIDR subnet. None of these tasks individually justify installing another application. But over time, I ended up with a collection of bookmarks to different websites, each solving one small problem. There was also another issue: privacy. Sometimes the data I'm working with isn't something I necessarily want to paste into an unknown third-party website. So I decided to build an alternative. The constraint: one HTML file I wanted the entire application to exist as a single file. No backend. No npm install. No CDN dependencies. No external API calls. No account. No telemetry. You download the HTML file, open it in a modern browser, and everything runs locally. The final file ended up at approximately 133 KB and contains 31 developer tools. What's inside? The tools are organized into six categories. Encode / Decode JSON Formatter & Validator Base64 Encode / Decode URL Encode / Decode HTML Escape / Unescape JWT Decoder Number Base Converter Generators UUID Generator Password Generator with entropy estimation Hash Generator Slug Generator Lorem Ipsum Generator Random Data Generator Converters Timestamp Converter CSV ↔ JSON JSON ↔ YAML CSS Unit Converter Case Converter Cron Expression Parser CSS Tools Color Picker & Converter Gradient Generator Box Shadow Generator Border Radius Generator CSS Filter Generator Text Tools Regex Tester Markdown Preview Text Diff Character Counter Text Sort & Dedupe String Inspector SQL Formatter Network Tools IPv4 Address and CIDR/Subnet Calculator Everything happens inside the browser. Making a single HTML file feel like an application I didn't want the result to feel like 31 unrelated forms dumped onto one page. So I added some application-level functionality. There's a Ctrl+K / Cmd+K command palette for quickly jumping between tools. The sidebar org