HowToCodePage

Technical SEO and measuring it

Canonicals, redirects, Core Web Vitals and the Search Console reports that tell you what is actually broken.

Canonicals and duplicate URLs

The same content is reachable from many URLs: with and without www, with and without a trailing slash, uppercase paths, tracking parameters, and http versus https. A canonical tag declares which one is authoritative so signals consolidate on a single URL instead of being split across five.

<!-- on every duplicate variant, point at the same target -->
<link rel="canonical" href="https://example.com/guides/wireless-headphones">

<!-- and enforce it in the server layer, not just in markup -->
# nginx
# return 301 https://example.com$request_uri;   # drop http and www once
  • A canonical is a hint, not a directive - keep the alternative URLs out of internal links as well.
  • Redirect chains waste crawl budget: link directly to the final URL rather than through two 301s.
  • Use hreflang for language and region variants so translated pages are not treated as duplicates.
  • Never canonicalise a whole section to the homepage; that removes those pages from the index.

Core Web Vitals

Core Web Vitals measure the experience of loading and using the page. They are evaluated at the 75th percentile of real visits, so a fast median cannot hide a slow tail.

MetricMeasuresGood threshold
LCP (Largest Contentful Paint)When the main content appears2.5 s or less
INP (Interaction to Next Paint)Responsiveness to taps and clicks200 ms or less
CLS (Cumulative Layout Shift)How much the layout jumps0.1 or less
/* reserve space for media to avoid layout shift */
img { width: 100%; height: auto; aspect-ratio: 16 / 9; }

/* defer non-critical fonts; a font swap reflows the whole page */
@font-face { font-family: Inter; src: url(/inter.woff2) format("woff2"); font-display: swap; }

The three fixes that pay off most often: preload the LCP image, serve images at the size they are displayed (AVIF or WebP), and stop third-party tags from blocking the main thread.

Measuring in Search Console

Search Console is the only place you see how the engine actually treated your site. Check it on a schedule rather than after a traffic drop.

  • Pages report: which URLs are indexed, excluded, or blocked, with a reason for each - your to-do list.
  • Performance: queries and pages over time, with average position; filter by country and device to find page-two pages worth improving.
  • Sitemaps: submission status and the number of discovered URLs; compare it against what you expect to exist.
  • Core Web Vitals: field data grouped by URL group, so you can fix the template rather than a single page.
  • Manual actions and Security issues: check these first when rankings collapse overnight.

Pair it with a log check: a 404 that appears in the Pages report because something links to a URL that used to exist is a one-line redirect fix.

⚠️
Judge performance on field data (real visitors, over 28 days), not on a single Lighthouse run. Lab scores vary by machine and network, and a green lab score with a red field report means real users are still waiting.

FAQ

Should www or the bare domain be canonical?
Either works, as long as you pick one and redirect the other permanently. The bare domain needs an A or ALIAS record and a certificate that covers it; www is easier to make resilient if you expect heavy traffic.
My pages turned to 'noindex' by accident - what now?
Remove the directive, deploy, then request indexing for the affected URLs. The Page report will keep showing the old status until those URLs are recrawled, which can take days.

On-page essentials Cache headers and cache keys

Last refreshed 2026-09-18.