The message Your preview will appear here means the preview process has not produced a working app yet. It is a symptom, not the root cause. The useful clue is usually the first red line in the terminal or browser console.

30-second answer

  1. Check whether the platform has an active incident.
  2. Open the project terminal and copy the first build or runtime error.
  3. Run npm run build to expose errors that the preview may hide.
  4. If the app uses a database or API, confirm that the required secrets exist in this project.
  5. Give the agent the exact error and ask it to change only the file or setting named by that error.

Do not keep pressing a generic fix button without reading the new result. If one attempt creates a different error, restore the last working version before trying another change.

Branch 1 — Is the platform unavailable?

Open the official status page first. If several projects stopped loading at the same time, or the status page reports a preview or build incident, wait for the provider to recover. Changing your code during an incident adds noise and can create a second problem.

If only one project fails, continue with the project checks below.

Branch 2 — Find the first terminal error

In Bolt, switch to Code view and open the Terminal tab. In any Vite-based project, run:

bash

npm run build

Read upward from the final failed or exit code 1 line and copy the first specific error. Common branches are:

  • Module not found or an import error: a file, package, or filename case does not match.
  • A syntax or type error: the most recent code change did not compile.
  • A missing environment variable: the app starts before a required database or API setting exists.
  • A dependency error: the package is missing from the project or its versions conflict.

Paste that exact line into the agent chat with the instruction: “Explain the root cause first. Do not edit yet.” After the explanation matches the log, ask for one bounded change.

Branch 3 — The build passes but the preview is still empty

Open the browser developer tools and select Console, then reload the preview. Copy the first red runtime error. A clean production build can still fail in the browser because a secret is missing, an API request is blocked, or client code reads an undefined value.

If the project uses Supabase or another API, inspect the project’s current Secrets or environment settings. Confirm the variable names exactly, including any public prefix required by the framework. Never paste the secret value into a support post or AI prompt.

Next, test the preview in a Chromium browser with extensions and VPN temporarily disabled. If it works there, the project code is probably not the cause; re-enable one browser or network layer at a time.

Branch 4 — A configuration change caused it

If the failure began immediately after the agent edited vite.config.ts, routing, a proxy, or security headers, compare that change with the last working version. Restore the last working checkpoint when you cannot explain the change. Then reapply only the smallest required setting.

Avoid resetting the entire project. A version rollback is safer because it gives you a known-good baseline and makes the breaking change visible.

Verify the fix

A preview image alone is not enough. Confirm all four checks:

  1. npm run build finishes without an error.
  2. The browser console has no new red exception after reload.
  3. The first screen renders and its main button or form responds.
  4. A second browser or private window loads the same preview.

If the preview works only in one browser, keep investigating extensions, cache, VPN, or network policy instead of changing app code.

If it still does not work

Restore the last working version and reproduce the failure with one small change. Save the terminal error, console error, tool name, browser, and the step that triggered it. Send those details to the platform’s official support channel. Do not include API keys, access tokens, project secrets, or personal data.

Beginner summary

Do not ask the AI to “fix everything.” Open the terminal, copy the first red error, and ask what caused that exact line. Run npm run build, check required secrets, and make one change. If the new attempt breaks more things, roll back to the last version that worked.