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name: check-posthog-loading description: > Inspect how the PostHog JavaScript SDK is loaded across a list of URLs. Use to confirm consistent installation across pages, find pages missing the snippet, detect mismatched API keys or hosts between pages, and verify the load method (head snippet vs deferred vs array.js).

Check PostHog loading

For each URL, navigates a real browser to the page, waits for PostHog to initialize, and reports:

• Whether window.posthog is defined and __loaded.
• Which load method was used: head_snippet, snippet, array_js_only, or none.
• Where in the document the snippet lives (head / body).
• The init config: api_key, api_host, person_profiles.
• Runtime state including the assigned distinct_id.

When to use

• Sanity-check a fresh install — does the snippet actually load on every page?
• After a page-template change — did one page lose the snippet?
• When investigating split data — are some pages pointing at a different api_host or api_key than others?
• Onboarding a new customer — confirm SDK is wired up before debugging events.

How to invoke

Call the check_posthog_loading MCP tool with:

• urls (required) — list of URLs to inspect.
• posthog_host (default https://us.i.posthog.com).

Returns a structured summary with which URLs loaded successfully, which didn't, and the load-method distribution.

Interpreting the result

Look for these red flags:

• Empty loaded list, full not_loaded list — snippet not present anywhere. Re-run install or check that the layout includes the snippet.
• Mixed loaded / not_loaded — snippet missing from some pages. Common cause: a page rendered by a different template or layout.
• Multiple distinct api_key values across pages — a page is pointing at the wrong PostHog project.
• Multiple distinct api_host values — a page is pointing at the wrong ingestion endpoint (e.g. EU cloud vs US cloud, or vs a self-hosted reverse proxy). This causes events to land in different projects than expected.
• load_method: array_js_only with no init config — array.js was loaded but posthog.init() was never called. Common with manual installs that miss the second half.