How to Build a Browser Extension for Passive Data Collection

Browser extensions can passively collect pricing data, track inventory changes, and monitor competitor updates as you browse. Here's how to build one that collects structured data from any website you visit. Use Cases for Passive Collection Price monitoring : Automatically log prices as you browse e-commerce sites Job market research : Capture salary data from job postings you view Competitive analysis : Track competitor feature changes over time Research aggregation : Collect data points across academic sources Extension Architecture Our extension has three parts: Content script — Runs on every page, extracts structured data Background service worker — Manages storage and API sync Popup UI — Shows collection status and stats The Manifest (manifest.json) { "manifest_version" : 3 , "name" : "Data Collector" , "version" : "1.0" , "permissions" : [ "storage" , "activeTab" ], "content_scripts" : [ { "matches" : [ "<all_urls>" ], "js" : [ "content.js" ] } ], "background" : { "service_worker