How I Built a Chrome Extension at a YC Startup

In September 2024, I joined Fuse AI — a YC W25 company building AI-powered sales automation. My first project: build a Chrome extension that could automate 40% of a sales rep's daily tasks.

Why a Chrome Extension?

Sales reps live in their browser. CRM tabs, LinkedIn, email, calendar — everything is a web app. A Chrome extension sits on top of all of these, watching what the user does and offering intelligent assistance.

The Architecture: Next.js + Chrome APIs

Yes, you can build Chrome extensions with Next.js. The trick is the extension popup and side panel are just web pages.

extension/
├── manifest.json
├── popup/              # Next.js static export
├── sidepanel/          # Same — static export
├── background.js       # Service worker
└── content-scripts/    # Injected into web pages

The background service worker handles Chrome API calls. The popup and side panel are React apps that communicate via chrome.runtime.sendMessage.

The Hardest Part: Content Scripts

Content scripts run inside the page's DOM but in an isolated JavaScript world. For LinkedIn automation, we needed to detect pages, extract data, and fill fields — all while LinkedIn aggressively changes DOM class names.

We built a resilient selector system using data attributes and ARIA labels instead of class names.

What Worked

Static export from Next.js — fast popup loads
Message passing pattern — clean separation between UI and Chrome APIs
Feature flags — gradual rollout for Chrome Web Store reviews

What Didn't

Manifest V3 service workers — they go idle after 30 seconds
Chrome Web Store reviews — one took 3 weeks
Content script isolation — debugging goes to a different DevTools panel

The Result

40% task automation rate. The extension became Fuse AI's core product surface.

I build production web apps and AI tools. See my work at 4ugusta.dev or hire me through 4UGUSTA Systems.