Chrome Side Panel API: Build a Sidebar Extension (2026) | ExtensionBooster

Short summary

The Chrome Side Panel API (stable since Chrome 114) provides a native persistent sidebar that lives outside the page DOM, avoiding CSS conflicts and style breakage from content scripts. Setup requires Manifest V3 with sidePanel permissions and a default_path, plus setPanelBehavior() in your service worker to toggle from the toolbar icon. The API supports per-tab panels via setOptions(tabId), enabling different content for different sites, with global defaults applying when no per-tab override is set.

• •Side Panel API creates a persistent, native sidebar isolated from page CSS/JS—no conflicts or state loss on tab navigation
• •Configure via Manifest V3: add sidePanel permission, declare side_panel.default_path, call setPanelBehavior({openPanelOnActionClick: true}) in service worker
• •Per-tab content is supported via setOptions(tabId, path)—show different panels for different sites with graceful fallback to global defaults

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