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 in this Gist. Here's a screenshot of the tool in action:

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