Simon Willison’s Weblog


Compare PDFs. Inspired by this thread on Hacker News about the C++ diff-pdf tool I decided to see what it would take to produce a web-based PDF diff visualization tool using Claude 3.5 Sonnet.

It took two prompts:

Build a tool where I can drag and drop on two PDF files and it uses PDF.js to turn each of their pages into canvas elements and then displays those pages side by side with a third image that highlights any differences between them, if any differences exist

That give me a React app that didn't quite work, so I followed-up with this:

rewrite that code to not use React at all

Which gave me a working tool! You can see the full Claude transcript plus screenshots of the tool in action in this Gist.

Being able to knock out little custom interactive web tools like this in a couple of minutes is so much fun.