Is your server slow to start responding?
It compares first-response samples, repeat requests and slower-page outliers.
What Check Engine measures
The check needs at least 3 positive response-time samples from successful pages. It compares the median with 0.8 seconds and 1.8 seconds. Above 1.8 seconds is medium severity when the repeat-request median is at most 0.8 seconds. Otherwise it is high. A median above 0.8 seconds and at most 1.8 seconds produces medium severity. At a median of 0.8 seconds or less, pages above 1.8 seconds can produce a low outlier finding when their share is below 0.3. For example, a slow first request followed by a repeat median of 0.8 seconds meets the warm-cache limit.
The check uses recorded first-response times and any positive repeat-request times. It compares the sampled requests. Review their timing and cache state before drawing conclusions about a visitor's experience.
How to read the result
Severity depends on the measured pattern. A fast repeat can point to a cache effect. Consistently slow medians call for a different review. Keep the first and repeat measurements together when reading the result.
Why it matters
The first byte is an early part of delivering a page. Comparing cold and repeated requests can help distinguish a cache effect from a broader response problem, without claiming that the test observed a particular visitor's connection.
How to fix it
Inspect slow templates and compare repeat requests before choosing a fix. Review server work, cache setup and cache expiry where the measurements point to them. Measure representative URLs again after changes. Check browser rendering and resource loading separately when reviewing the complete page experience.
How to reduce server response time (TTFB)
What we found in field audits
Problems in Speed & Core Web Vitals were found on 13 of the 14 sites we audited. These are area totals. Read the field-audit method.
Method note
backend/seo_engine/checks/performance.py, ttfb, revision 0bb8e8d3.
Common questions
Is a first-response median of 0.8 seconds too slow?
No. At 0.8 seconds, the site median stays within the fast group. Individual slower pages can still qualify for an outlier result.
When can a slow first response get medium rather than high severity?
A first median exceeding 1.8 seconds gets medium severity if the repeat median does not exceed 0.8 seconds. Otherwise it gets high.
How many response-time samples does the TTFB check need?
The minimum is 3 positive response-time samples. They must come from successful pages; zero or missing timings do not fill the sample.