PDF Handouts

Checking the claim yourself

A web page cannot prove its own innocence. Any reassuring badge it shows you would look exactly the same on a page that was uploading your files. So rather than ask you to trust a claim, here are four ways to check it — none of which rely on anything this page tells you.

1. Pull the plug

   Once this page has loaded, disconnect from the internet — turn off wi-fi, or use your browser's offline mode. Now add your files and build. It still works. Nothing that needs a server could do that.

2. Watch the network

   Open your browser's developer tools, go to the Network tab, clear it, then build a handout. There are no requests. The only traffic this page ever makes is fetching itself when it first loads.

3. Make it try to leak, and watch it fail

   This page ships a Content Security Policy that the browser enforces — the page cannot switch it off or work around it. You can read it near the top of the page source. To see it working, paste this into the developer console and watch every attempt get refused:

   fetch('https://example.com/x', {method:'POST', body:'test'});
   new WebSocket('wss://example.com/x');
   navigator.sendBeacon('https://example.com/x', 'test');
   new Image().src = 'https://example.com/x?d=test';

   Browsers make you type allow pasting in the console once before they let you paste anything — a sensible precaution you should keep. Nothing above sends real data; it only tries to reach a dummy address so you can see the refusal.

4. Read it, or build it yourself

   The whole thing is open source. The page is a few hundred lines of plain JavaScript with no dependencies and no build step, so what you see in the source is exactly what runs. The PDF engine is Rust compiled to WebAssembly, and you can compile it yourself from the same source and compare it against what is served here.

   Source on GitHub — the same tool is also a command-line program, if you would rather not use a browser at all.

One honest caveat: the policy permits requests back to the origin this page came from, because that is how the WebAssembly module itself is loaded. That origin is GitHub Pages, which serves static files and has nothing on the other end that could receive an upload — but if that is not good enough for your documents, use the command-line version, which has no network code at all.