Built because the upload step was the problem

Most PDF tools online are a thin form in front of a server: you upload a document, a queue somewhere processes it, and you hope the cleanup job runs before your file sits around longer than it should. That model is also why file size caps and "5 tasks per day" limits exist — they're rationing someone else's compute.

pdfslash moves the work to the only computer that should ever see your document: yours. The libraries doing the actual page manipulation are compiled to WebAssembly and run inside this browser tab. There's no daily limit to relax and no server cost to recover, so there's nothing pushing toward a paywall.

That's also why tools like OCR work the same way on slow hotel WiFi as they do offline entirely. The processing was never going anywhere in the first place.