Reduce the impact of third-party code

What’s actually happening

You've optimized your own code and the score still won't move. The audit table lists each third party by name — Google Tag Manager, Google Analytics, Facebook, Intercom, Hotjar — with its transfer size and main-thread blocking time. Lighthouse fails the check once combined blocking time crosses 250ms. The pain is worst on first load because these scripts often run synchronously during startup.

Common causes

• A tag manager (GTM) that loads a pile of additional tags, each with its own script and main-thread cost.
• Analytics, session-replay, or heatmap scripts (Hotjar, FullStory, PostHog) that instrument the page eagerly on load.
• A live-chat widget (Intercom, Drift, Zendesk) that pulls a large bundle and an iframe before the user ever clicks it.
• Ad and consent-management scripts that block rendering while they negotiate.
• Embedded widgets — YouTube iframes, social buttons, maps — each booting their own framework.

How to fix it

1. Identify the worst offenderSort the third-party table by main-thread blocking time. One or two entities usually account for most of it. Fix those before touching anything else — the long tail rarely matters.
2. Facade the heavy widgetsReplace chat, video, and map embeds with a lightweight placeholder (a static image or styled button) that only loads the real script on click or hover. lite-youtube-embed and react-lite-youtube-embed are drop-in examples; most chat vendors document a deferred-load snippet.
3. Defer and lazy-loadAdd defer to non-critical third-party tags, and trigger analytics/replay scripts after the load event or on first interaction rather than during startup. In GTM, move tags off the All Pages / Page View trigger to Window Loaded.
4. Self-host what you canServing a script from your own domain skips a separate DNS/TCP/TLS handshake and lets you cache it. Google Analytics' gtag and many font/script files can be proxied or self-hosted.
5. Audit and cutRun a regular inventory of installed tags. Marketing tools accumulate; half are usually unused. Delete the ones nobody reads anymore.