500+ Free Online Tools I Built — Here Are the Most Useful Ones

Over the past year, I've been building free browser-based tools at devtools-site-delta.vercel.app . What started as a JSON formatter I built for myself has turned into 500+ tools. Most of them run entirely client-side — your data never leaves your browser. No accounts, no paywalls, no "5 free uses per day" nonsense. Here are the 15 I use the most. 1. JSON Formatter & Validator /json-formatter Paste in ugly JSON, get it pretty-printed with syntax highlighting. Also catches errors and tells you exactly where the problem is (line and character). I use this multiple times a day when debugging API responses. 2. PDF Merge /pdf-merge Drag in multiple PDFs, reorder them, merge into one file. Runs entirely in your browser using pdf-lib. No upload, no server. I wrote a whole post about this one . 3. Image Compressor /image-compress Drop in an image, adjust the quality slider, download a smaller version. Uses the Canvas API. I compress every image before adding it to a blog post or README. Usuall