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PostHog Toolbar or Heatmaps Not Loading

Workaround available Web Updated October 21, 2026

Quick answer

The PostHog toolbar (needed for heatmaps) fails when the page URL isn't authorized, CSP or an ad blocker blocks it, or ui_host isn't set behind a reverse proxy. Authorize the URL, allow PostHog in CSP and set ui_host.

Most likely fix: Authorize the URL.

Symptoms

Launching the toolbar opens your site without the toolbar, heatmaps show nothing, or the console shows 'source URI is not allowed'.

Why it happens

  • Page URL not in the toolbar's authorized URLs
  • Content Security Policy blocking the toolbar script or API
  • Ad blocker
  • Reverse proxy without ui_host set
  • Frontend overwriting the #__posthog URL hash
  • Wrong regional assets host for EU projects

How to fix it

Try these in order — the most common fix is first.

  1. 1. Authorize the URL

    1. In PostHog, open Launch Toolbar
    2. Add the exact URL of your site and click Save, then Launch

  2. 2. Fix proxy and region settings

    1. Set ui_host to https://us.posthog.com or https://eu.posthog.com in posthog.init()
    2. EU projects should use eu-assets.i.posthog.com for assets

  3. 3. Unblock the toolbar

    1. Allow PostHog domains in your CSP (Firefox is stricter than Chrome)
    2. Disable ad blockers while using the toolbar

  4. 4. Handle routers that rewrite the hash

    1. Read the __posthog value from the URL hash before your router changes it
    2. Call posthog.loadToolbar() with it

This guide also covers

  • posthog toolbar not loading
  • posthog heatmap not showing
  • posthog heatmaps not working
  • posthog toolbar not appearing

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