Interactive Signals Test
The Time to Interactive Test measures the moment your page becomes reliably interactive — when visible content has loaded, event handlers are registered for visible elements, and the main thread is quiet enough to handle user input within 50 ms. Slow TTI is a hidden killer: the page looks loaded but tapping a button does nothing, leaving users frustrated. The fix is almost always about reducing JavaScript: fewer scripts, smaller bundles, deferred third parties.
What This Tool Checks
- TTI timing in headless Chrome
- JavaScript bundle size
- Long tasks (>50 ms) on the main thread
- Third-party scripts blocking interactivity
- Hydration cost on SSR pages
- Code-splitting opportunities
Why It Matters for SEO
TTI sits between "page looks loaded" and "page actually works". A poor TTI means users tap a button, nothing happens, they tap again, and bounce. Lighthouse uses TTI as one of its core metrics, and it correlates strongly with INP — the new Core Web Vital. Improving TTI almost always improves INP and overall page-experience scores in turn.
How to Fix It
Code-split your JavaScript so only what is needed for the current page is loaded. Defer third-party scripts. Audit polyfills and remove what is no longer needed. Reduce hydration cost by hydrating only interactive components (islands architecture). Re-test until TTI drops below 5 seconds on mobile.
How It Works
Headless Chrome navigates the URL, captures the TTI metric (last long task on the main thread before quiet), and walks the JavaScript execution timeline to attribute every long task to its source script. The report sorts opportunities by execution time so you target the biggest wins first.
Common Mistakes to Avoid
- Synchronous third-party scripts in <head>
- Massive JavaScript bundles (no code splitting)
- Heavy SSR hydration on every page
- Polyfills loaded for browsers that no longer need them
- Tag managers loading dozens of additional scripts
Quick Checklist
- TTI under 5 seconds on mobile
- JavaScript bundle under 200 KB transferred
- No long tasks above 200 ms
- Third-party scripts deferred
- Hydration scoped to interactive islands