Get your handwritten math marked up like a teacher would
A calculus student built penmentor: press a key while working by hand in Xournal++ and Claude, Codex or Gemini marks up the page with hints instead of answers. It runs on the AI command-line agent you already use, on that subscription.
Source
abdullahalharir on Hacker News · 2026-10-20 · Project link
Written in our own words. Credit to the original author. Link checked 2026-10-20.
What they did
A calculus student built penmentor: press a key while working by hand in Xournal++ and Claude, Codex or Gemini marks up the page with hints instead of answers. It runs on the AI command-line agent you already use, on that subscription.
Result (as claimed)
40 points on Hacker News; open source on GitHub.
Tools they used
Cost: Claude Code: from $17/mo; OpenAI Codex: free plan, paid from $8/mo.
Set it up
Gather your sources
Collect the papers, notes, links or files you want to work from in one place.
Load them into the tool
Open Claude Code, OpenAI Codex, Antigravity, Xournal++ and add your sources. Keep the original files so you can check claims later.
Ask focused questions
Ask for summaries, comparisons or connections with citations to the source passages.
Verify and save
Spot check claims against the sources, then save the output as notes you can reuse.
Copy the full setup prompt
Paste into your agent and it will walk you through the setup, asking before anything that sends, posts or spends.
You are helping me set up this AI use case end to end in Claude Code. Goal: Get your handwritten math marked up like a teacher would What the original author did: A calculus student built penmentor: press a key while working by hand in Xournal++ and Claude, Codex or Gemini marks up the page with hints instead of answers. It runs on the AI command-line agent you already use, on that subscription. Reported result (as claimed by the author): 40 points on Hacker News; open source on GitHub. Source: https://news.ycombinator.com/item?id=50167604 Tools they used: Claude Code, OpenAI Codex, Antigravity, Xournal++ Category: Research & learning Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
You are helping me set up this AI use case end to end in Codex. Goal: Get your handwritten math marked up like a teacher would What the original author did: A calculus student built penmentor: press a key while working by hand in Xournal++ and Claude, Codex or Gemini marks up the page with hints instead of answers. It runs on the AI command-line agent you already use, on that subscription. Reported result (as claimed by the author): 40 points on Hacker News; open source on GitHub. Source: https://news.ycombinator.com/item?id=50167604 Tools they used: Claude Code, OpenAI Codex, Antigravity, Xournal++ Category: Research & learning Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
You are helping me set up this AI use case end to end in Grok Bot. Goal: Get your handwritten math marked up like a teacher would What the original author did: A calculus student built penmentor: press a key while working by hand in Xournal++ and Claude, Codex or Gemini marks up the page with hints instead of answers. It runs on the AI command-line agent you already use, on that subscription. Reported result (as claimed by the author): 40 points on Hacker News; open source on GitHub. Source: https://news.ycombinator.com/item?id=50167604 Tools they used: Claude Code, OpenAI Codex, Antigravity, Xournal++ Category: Research & learning Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
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Guides for this use case
How to build with Gemini 4 Argon and Gemini agents · How to use Claude Code and Codex together · How to replace SaaS subscriptions with vibe-coded tools · How to use AI agents for taxes, bills and budgets
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