Pull passages out of any PDF onto a notes canvas, write what you think, and link ideas with labels like "supports" or "contradicts". Click any note to jump back to its exact page. Export the whole map as AI-ready Markdown and give it to ChatGPT or Claude with the PDF. Free, open source, no account, and nothing leaves your browser.
I built this for reading papers and textbooks. Highlights in a PDF pile up with no structure; notes apps lose track of where a quote came from. Marginalia keeps both: a canvas of linked excerpts where every card remembers its page. The Markdown export is the part I didn't expect to love: it gives an AI your structure and your notes, not just the raw document. It's MIT licensed and runs entirely in your browser. Feedback very welcome.