I Built a Chrome Extension That Generates AI Replies for LinkedIn, X and Threads — Here's What I Learned

Building Replygen started as a personal itch. As a solo SaaS founder, I needed to stay consistently active on LinkedIn, X, and Threads to drive organic distribution — but crafting thoughtful replies at scale was burning time I didn't have. So I built an AI engagement co-pilot that lives in your browser and suggests context-aware replies as you scroll your feed.

This post is a technical walkthrough of the key architecture decisions, the unexpected challenges, and the lessons that only come from shipping a real Chrome extension to production users.

The Core Architecture

The extension follows the standard content script + background service worker pattern:

Content script — injected into LinkedIn/X/Threads DOM. Handles UI injection (the suggestion overlay), reads post content via DOM selectors, sends data to the background worker via chrome.runtime.sendMessage