About

PDFs can hide content that isn't visible on the page: text painted white on white, layers turned off by default, font sizes shrunk to nothing, or instructions tucked in off-page coordinates. As more documents get summarized or reviewed by AI tools, this hidden content has become a way to slip instructions past a human reader and straight to the model reading the file on their behalf.

PDF Stowaway Scanner checks a PDF for these techniques: invisible render modes, white-on-white text, tiny fonts, crop box mismatches (the signal left behind when content is cropped off the page), hidden optical content groups, embedded files, JavaScript, and known prompt-injection phrasing. Everything runs in your browser using WebAssembly. Your file is never uploaded anywhere.

This is a free, open-source tool. It won't catch everything, and it isn't a substitute for careful review, but it surfaces the signals that are easy to miss by eye.