I built a Claude AI sidebar extension for the browser — here’s how

I spend a lot of time reading docs, articles, and research papers. The constant tab-switching to ask Claude about what I'm reading was killing my flow. So I built a Chrome extension that injects a Claude-powered sidebar into every webpage. What it does Summarize — one click to get the full page summarized Key points — bullet-point extraction of the most important info Explain selection — highlight any text, get an explanation Improve selection — highlight text you've written, get a rewrite Chat — full conversational mode with the page content as context Alt+A toggles it open/closed from anywhere. Technical stack Manifest V3 Chrome extension Shadow DOM for UI isolation (no style conflicts with host pages) Service worker background script for Claude API calls anthropic-dangerous-direct-browser-access header for direct API calls Claude Haiku for speed, Sonnet for longer outputs The CORS issue I hit Calling Claude API directly from a browser extension causes a CORS error unless you add the