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The core concept is a tool to let users think through every word, sentence and line of dense technical textbooks in pdf form. I can't find a single app that allows you to reason about words and sentences while recording down your thoughts in a friction free way.

All the note taking apps I've used treat paragraphs and pages as the main grouping element but anyone who's studied hard things knows that tough ideas are built up in groups of words at a time. Missing just one sentence before makes it impossible to understand the concepts further down.

I wanted a way to let myself and others jot down ideas and partial understanding quickly and inline with the actual line that I'm struggling with. This lets me walk away from a problem and never lose any progress I made. It's almost like save checkpoints.

The app also has another very nice scratchpad feature that lets you group notes from different areas of the textbook that talk about the same concept. It lets you relate topics from different parts of the textbook to form a cohesive picture of the material.

I've also integrated Excalidraw into the scratch pad so you can take excalidraw diagram notes along with your note taking

As an appreciation to Hacker News users for feedback, I made this pay what you want link as a token of appreciation. I've worked many sleepless nights to get this app as polished as it is and being able to afford to do this on my free time would be nice.

The main product page is https://marginstudy.app/. Would really appreciate feedback