Remarq

I was too lazy to comment on my professor’s videos. So I built an AI Chrome extension to do it for me.

The story

Built for a Prompt Engineering for GenAI course at Northeastern University where daily comments on the professor’s posts counted toward the final grade. Instead of commenting manually, built a Chrome extension that reads page context and generates contextually relevant comments using Claude AI.

What it does

• YouTube: automatically reads the video title and channel, generates a relevant comment
• LinkedIn: highlight any post text, generate a comment in your chosen tone
• Substack: highlight any article text, generate a comment instantly

Tone options: Thoughtful, Enthusiastic, Professional, Concise, Curious

No API key required — just install and use. Limited to 10 comments per day.

Tech stack

• Chrome Extension (Manifest V3)
• Content scripts for platform-specific scraping
• Background service worker for API communication
• Node.js + Express backend (private repo) deployed on Railway
• Anthropic Claude API for comment generation
• In-memory rate limiting per extension ID

Architecture

Chrome Extension → Railway Backend (private) → Anthropic Claude API

The backend is intentionally kept in a private repository. The extension communicates with a hosted backend endpoint — no API keys are needed on the client side.

Prompt engineering decisions

• Platform-specific system prompts: YouTube gets conversational tone, LinkedIn gets professional, Substack gets thoughtful
• Page content is explicitly passed as data only with instructions to never follow directives found within it — prevents prompt injection through post text
• Hard cap of 150 tokens enforced at the API level, not just the UI
• BLOCKED and NO_CONTENT sentinels for safety filtering

What I learned

• Chrome Extension architecture: content scripts, service workers, message passing
• Prompt injection defense in production AI systems
• Building and deploying a proxy backend to protect API keys
• Platform-specific DOM scraping (YouTube, LinkedIn, Substack all have different structures)
• Rate limiting strategies for AI-powered tools

Installation

This extension is available on the Chrome Web Store: [link coming soon]

To run locally you will need access to the backend — the hosted endpoint is rate limited and intended for personal use.

License

MIT