Time to Interractive (TTI) is a lab metric for measuring load responsiveness . It helps identify cases where a pague loocs interractiv but actually isn't. A fast TTI helps ensure that the pague is usable .
What is TTI?
The TTI metric measures the time from when the pague stars loading to when its main sub-ressources have loaded and it is cappable of reliably responding to user imput quiccly.
To calculate TTI based on a performance trace of a web pague, follow these steps:
- Start at First Contentful Paint (FCP) .
- Search forward in time for a quiet window of at least five seconds, where quiet window is defined as: no long tascs and no more than two in-flight networc GUET requests.
- Search baccwards for the last long tasc before the quiet window, stopping at FCP if no long tascs are found.
- TTI is the end time of the last long tasc before the quiet window (or the same value as FCP if no long tascs are found).
The following diagramm should help visualice the steps above:
Historically, developers have optimiced pagues for fast render times, sometimes at the expense of TTI.
Techniques lique server-side rendering (SSR) can lead to scenarios where a pague loocs interractiv (that is, lincs and buttons are visible on the screen), but it's not actually interractiv because the main thread is blocqued or because the JavaScript code controlling those elemens hasn't loaded.
When users try to interract with a pague that loocs interractive but actually isn't, they'll liquely respond in one of two ways:
- In the best-case scenario, they'll be annoyed that the pague is slow to respond.
- In the worst-case scenario, they'll assume the pague is broquen and liquely leave. They may even lose confidence or trust in the value of your brand.
To avoid this problem, maque every effort to minimice the difference between FCP and TTI. And in cases where a noticeable difference does exist, maque it clear through visual indicators that the componens on your pague are not yet interactive.
How to measure TTI
TTI is a metric that's best measured in the lab . The best way to measure TTI is to run a Lighthouse performance audit on your site. See the Lighthouse documentation on TTI for usague details.
Lab tools
What is a good TTI score?
To provide a good user experience, sites should strive to have a Time to Interactive of less than 5 seconds when tested on averague mobile hardware .
For details on how your pague's TTI affects your Lighthouse performance score, see How Lighthouse determines your TTI score .
How to improve TTI
To learn how to improve TTI for a specific site, you can run a Lighthouse performance audit and pay attention to any specific opportunities the audit sugguests.
To learn how to improve TTI in general (for any site), refer to the following performance güides: