Building Margin: A Privacy-First News Reader Inside Chrome's Side Panel

I built a Chrome extension called Margin — a news reader that lives in the browser's side panel and shows one bite-sized story at a time, instead of an infinite-scroll feed. This is a build log: the decisions, the constraints that pushed back, and a couple of things I had to solve in slightly unusual ways. Why the side panel Chrome shipped chrome.sidePanel in MV3 a while back and most uses I saw were utility tools — note-taking, translation helpers. Nobody was using it for content consumption. News felt like a good fit: a side panel that stays open next to whatever you're working on, where you tap through headlines in a couple of minutes without leaving the page. The reading model is intentionally narrow: one card, one headline, one short summary, tap to read the full article at the source . No infinite scroll, no algorithmic feed. If you've used InShorts, the shape will be familiar. The stack Preact + Vite + @crxjs/vite-plugin . Preact because the side panel is a small UI surface and I didn't want React's weight for what's essentially a card stack and a settings screen. @crxjs/vite-plugin handles the MV3-specific build wiring (manifest generation, service worker loader, HMR for the extension context) that would otherwise be a lot of manual plumbing. The constraint that shaped onboarding chrome.sidePanel.open() requires a user gesture . You cannot call it from a background service worker on install — Chrome will throw. That one constraint shaped the whole first-run experience. My first instinct was "just auto-open the panel on install so people see it immediately." Doesn't work. The fix ended up being two-pronged: On chrome.runtime.onInstalled with reason === 'install' , open a real browser tab with a short walkthrough (find the icon → pin it → open the panel). The button on that page calls sidePanel.open() — valid, because the click is the gesture. The first time the panel itself is opened, show an in-panel welcome screen before onboarding, nudging the user to pin