Stackblitz Live Preview refresh failures: step‑by‑step diagnostic guide

Live Preview stalls in Stackblitz – diagnostic guide

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Problem: You're editing a file in Stackblitz's web IDE, but the Live Preview pane stays blank or shows the old code. No changes appear even after saving.

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Takeaway: Before digging into settings, verify that the WebSocket connection to wss://preview.stackblitz.io is alive and that no build or cache issue is blocking the update.

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Recognizable condition

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Live Preview not updating after file edits.

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Diagnostic table

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Likely cause	Quick symptom check
WebSocket blocked	No wss:// preview.stackblitz.io connection in DevTools Network
File watcher skipped	Terminal shows no watcher activity
Build not triggered	Build output panel empty or failed
Browser cache stale	Preview unchanged after edits
Project size throttling	Size warning on project dashboard
Custom dev server misconfigured	Preview fails to load custom assets

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Ordered checks

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1. \n

   WebSocket connectivity. Open the browser's Developer Tools Network tab, filter by ws or wss, and confirm a persistent connection to wss://preview.stackblitz.io. If the connection is absent or drops immediately, a network proxy or firewall may be blocking it. Where to run: Any browser with DevTools enabled on the Stackblitz project. Required permissions: None; the IDE and browser handle the connection. Expected check: A stable connection with periodic message frames. Relevant risk: Closing the DevTools tab terminates the inspection session but not the underlying connection.

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   File watcher status. Stackblitz automatically watches source files for changes. If a file is locked, binary, or exceeds watch limits, updates may not trigger. Open the integrated terminal; look for watcher startup messages. Where to run: Stackblitz terminal tab. Required permissions: None. Expected check: No watcher error lines; the watcher is active. Relevant risk: Misinterpreting normal startup noise as a problem.

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   Build trigger. Click the Build button in the UI or press Ctrl+Shift+B. Observe the Build output panel. If the build fails or is skipped, the preview won't refresh. Where to run: Stackblitz web IDE. Required permissions: None. Expected check: Successful build log entry with no errors. Relevant risk: Repeated builds consume project quota.

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   Browser cache. Open the project in an incognito window, or clear the browser cache for stackblitz.io. Cached HTML/JS can serve stale preview content. Where to run: Browser settings or incognito window. Required permissions: None. Expected check: Preview updates in incognito window. Relevant risk: Incognito may disable some browser extensions that affect the IDE.

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   Project size. If the repository exceeds Stackblitz's implicit size limit (roughly 500 MB of source), live-update throttling may occur. Check the project dashboard for size warnings. Where to run: Project settings page within Stackblitz. Required permissions: None. Expected check: No size-warning banner. Relevant risk: Splitting the project may be required for large codebases.

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   Custom dev server. If using a custom dev server (e.g., webpack-dev-server) instead of Stackblitz's default, ensure it's configured to serve the preview context. Review .stackblitzrc for a serve command. Where to run: Project root, edit .stackblitzrc. Required permissions: Write access to the project's configuration files (handled by the IDE). Example serve config: serve: vite or { serve: vite }. Expected check: Custom server logs indicate listening on the preview port. Relevant risk: Incorrect config can break the preview entirely.

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Fixes tied to findings

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• WebSocket closed: Disable corporate proxy or switch to a network that permits wss://preview.stackblitz.io. If using a VPN, split‑tunnel the Stackblitz domain.
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• File watcher stale: Reload the project tab. Add a trivial comment to a source file and save to re‑engage the watcher.
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• Build not running: Ensure package.json includes a valid start script. Stackblitz defaults to Vite or Next.js; if custom, add a serve command to .stackblitzrc.
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• Caching: Incognito window usually resolves. If not, clear browser cookies for stackblitz.io.
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• Project size: Split the repository into micro‑modules, or remove dev dependencies not needed for preview.
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• Custom dev server: Update .stackblitzrc with the correct serve command, e.g., serve: vite or { serve: vite }.
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Escalation criteria

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If none of the above restore live preview after 30 minutes of troubleshooting, and the project uses a non‑standard dev server, contact Stackblitz support with the project ID and network configuration. Include the WebSocket logs from DevTools.

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Limitations

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• Stackblitz's internal build cache is not manually clearsable.
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• Project size limits may auto‑throttle live preview.
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• This guide assumes the default Stackblitz web IDE; command‑line or offline modes behave differently.
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• Custom dev servers may require additional configuration beyond this guide's scope.
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Verification – practical way

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After each fix, edit a source file, wait 2‑3 seconds, and confirm the preview updates. If using an incognito window, compare results between normal and private windows.

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