TTFB

  • Time to First Byte (TTFB) is the total amount of time spent to receive the first byte of the response once it has been requested. It is the sum of “Redirect duration” + “Connection duration” + “Backend duration”. This metric is one of the key indicators of web performance.
  • In the Waterfall Chart, it is calculated at the start of the test until just before receiving on the page request and represented by the orange line.
  • Some ways to improve the TTFB include: optimizing application code, implementing caching, fine-tuning your web server configuration, or upgrading server hardware.
  • In short Redirect Connect + Backend = TTFB
As Per Billy Hoffman:
  • To summarize, your ideal targets for your initial HTML page load should be:
    • Time to First Byte of 500 ms or less
    • Round Trip network latency of 100 ms or less
    • Back-end processing of 400 ms or less
For WP-engine:
  • So if your numbers are higher than this, what can you do about it?
    • A TTFB below 200ms is considered great.
    • A TTFB in the 200ms to 500ms range is considered normal and okay.
    • A TTFB consistently higher than 600ms will need to be investigated.
Troubleshoot steps for high TTFB:
  • Test the TTFB on a few different pages of your website
    • If it’s just a few pages that are slow, it’s likely an element that is being used in common across the pages
  • Test a static HTML file instead of a dynamic WordPress page
    • If TTFB is high on a static page, then there may be a load issue on the server.
    • If TTFB is low on a static page, then some content on your site is likely causing the issue
  • Activate a different theme
    • If TTFB is lower, your theme is likely causing the issue. Check for an update or reach out to the theme developer.
    • If TTFB is still high, try disabling plugins.
  • Deactivate all plugins
    • If TTFB is still high, it’s potentially due to a database issue.
    • If TTFB is lower, try enabling the plugins one by one to find the culprit.

First CPU Idle

  • First CPU Idle is one of six metrics tracked in the Performance section of the Lighthouse report. Each metric captures some aspect of page load speed.
  • What First CPU Idle measures:
    • First CPU Idle measures how long it takes a page to become minimally interactive. A page is considered minimally interactive when:
    • Most—but not necessarily all—UI elements on the screen are interactive, and
    • The page responds, on average, to most user input in a reasonable amount of time.
  • The Time to Interactive (TTI) metric measures how long it takes a page to become interactive. “Interactive” is defined as the point where:
  • The page has displayed useful content, which is measured with First Contentful Paint.
  • Event handlers are registered for most visible page elements.
  • The page responds to user interactions within 50 milliseconds.