Show HN: Penmentor – Claude marks up your handwritten math like a teacher
What happened
Penmentor is an open‑source tool that lets you write math by hand in the Xournal++ note‑taking app and, with a single key press, sends the page to an AI model such as Claude, Gemini or GPT. The AI then marks the work on the screen like a teacher, circling mistakes, ticking correct steps, offering hints, and can generate a 3Blue1Brown‑style animation of the concept using manim. The marks stay visible while you continue writing and can be cleared with Esc. It runs via a command‑line agent you already have, requiring a Claude (or similar) subscription and some Linux utilities. The repository includes a plugin, setup guide and self‑test script.
Why it matters
For students or anyone learning calculus, it provides immediate, visual feedback that mimics a personal tutor, helping concepts stick without waiting for a human teacher. It also lets users explore interactive animations of their problems, turning static notes into dynamic learning aids.
Reality check
An automated, sceptical read of the sourceIncremental. The project builds on existing AI assistants and Xournal++ integration, adding a convenient visual feedback layer rather than introducing a fundamentally new technology.
Is this a big deal?
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