Performance
Resource hint
Resource hint is an HTML `<link>` relation that tells the browser to do network work early: `dns-prefetch`, `preconnect`, `preload`, or `prefetch`. Hints are advice, and the browser may ignore them.
How it is measured
Inspect the head for `rel` values and the response for `Link` headers. In the waterfall, hinted requests start earlier than the parser would have found them. Each type has its own priority: preload is high, prefetch is lowest, and preconnect and dns-prefetch carry no payload at all.
Measure each hint against the metric it exists for: LCP for a hero preload, connect time for a third-party preconnect. Compare five runs before and after. If the metric does not move, the hint is cost without benefit.
Worked example
An audit of a travel blog finds 14 hints in the head: five preconnects, six preloads, two prefetches, and one dns-prefetch. The page's LCP image is not among them. Three of the preloaded fonts are never used, because the theme switched to system fonts last year.
After cleanup it keeps a preload for the hero JPEG and a preconnect for the image CDN. LCP drops from 3.8 s to 2.9 s, mostly because bandwidth now goes to the hero instead of dead fonts.
How it differs
A resource hint is the category, and preload is one member that forces a named file to download now. The other members only warm connections or fetch for later. Hints do not include `async` or `defer`, which change script execution rather than network scheduling.
Common errors
Treating hints as free. Leaving them in place after the page changed. Copying a hint block from a tutorial. Hinting resources that sit behind consent or login. Setting `as` incorrectly. Using many hints so that none stands out.
In practice
Print every hint on your top template and write down which metric each one serves. Delete the ones you cannot tie to an LCP or connect-time number. Re-test, then add hints back one at a time with the waterfall open.