Resource Hints Generator

Performance engineers tuning Largest Contentful Paint, SEO specialists fixing render-blocking font delays, and frontend developers who inherited a head full of missing crossorigin attributes all build the same set of link tags by hand and then debug double font fetches. This generator produces preload, prefetch, preconnect, dns-prefetch, and modulepreload markup with correct as and crossorigin attributes, plus the HTTP Link header form for edge delivery. Each hint is checked against the browser rules that cause silent drops and re-downloads.

Quick presets

Type

Href

crossorigin

HTML head tags

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HTTP Link header

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How the Generator Renders Hints and Checks Rules

Each hint is stored as a small record — type, href, as, type, crossorigin, referrerpolicy, media — and rendered twice: once into an HTML link tag and once into a semicolon-delimited Link header value. Attribute emission follows the browser contract: as and type only appear for preload and modulepreload, media only for preload, and crossorigin is written with its explicit value so same-origin font fetches still run in CORS mode. The Link header form wraps the URL in angle brackets and lists the same parameters after rel=.

The warning pass checks the rules that cause the most silent failures. A preload without as is ignored by the bucketing logic in Chromium. A font preload without crossorigin triggers a second non-CORS fetch. The same href preloaded and prefetched cancels the priority benefit. Preconnect hrefs must be absolute origins; more than four of them adds handshake work for hosts the page may never reach. Every warning names the browser behavior behind the rule.

Where to place the tags

Preload and preconnect tags work best as high as possible in the head, before stylesheets that could delay their discovery. Prefetch tags can sit anywhere because they are low priority. When the HTML itself is served by a CDN that supports early hints, the Link header form reaches the browser before the body arrives, which is the fastest path for LCP-critical assets.

as values and request modes

The as attribute tells the browser which request bucket the preload belongs to, and it must match the destination of the later real request. as="font" and as="fetch" force CORS mode, which is why crossorigin is mandatory there. Mismatching as — for example marking a .woff2 file as as="style" — causes the preload to be discarded and the font to load late through the normal path.

Before and after: fixing a late-loading font

Before (double fetch, preload warning)

<link rel="preload" href="/fonts/brand.woff2" as="font">
<link rel="preconnect" href="https://fonts.gstatic.com">

After (CORS mode + origin warm-up)

<link rel="preload" href="/fonts/brand.woff2" as="font" type="font/woff2" crossorigin="anonymous">
<link rel="preconnect" href="https://fonts.gstatic.com">
<link rel="dns-prefetch" href="https://fonts.gstatic.com">

Use Cases

Developer	Production	Workflow
Preload the LCP image discovered by CSS background	Send Link headers from the CDN edge before HTML	Audit a head full of unverified preload tags
Fix double font downloads caused by missing crossorigin	Cut preconnect origins down to the four that matter	Standardize hint patterns across template partials
modulepreload the JS entry chunk for an SPA shell	Prefetch the likely next route on idle time	Verify hint output after a framework upgrade

Common Mistakes and Troubleshooting

The most common mistake is preloading a resource the HTML already loads with fetchpriority="high", which wastes a connection slot. The second is a preconnect to the page's own origin; the connection is already warm, so the hint does nothing. The third is a preload URL that does not match the final request URL after redirects or fingerprinting, which makes the preload a wasted download.

If devtools shows a preload warning, compare the as value and crossorigin attribute with the real request's destination and mode. If a hint seems ignored, confirm the tag sits in the head and that the response does not already be full-body before the browser parses it. For Link headers, verify the header actually reaches the browser with the HTTP header parser.

Best Practices for Resource Hints

Preload only what the LCP or first interaction genuinely needs: one hero image, one display font, one blocking stylesheet. Match every font and fetch preload to crossorigin="anonymous". Keep preconnect to origins that serve those critical assets, and use dns-prefetch for everything else. Prefetch next-route assets on requestIdleCallback rather than at parse time. Re-check the hint set after every design-system or bundler change, because hashed asset URLs break stale preloads.

Pair this generator with the LCP image HTML optimizer for the image tag itself, the SRI hash generator for integrity on cross-origin files, the web vitals budget calculator to decide which hints are worth their bandwidth, the HTML head auditor for a full head review, and the link rel generator for canonical and alternate link tags.

Resource Hints Generator FAQ

What is the difference between preload, prefetch, and preconnect?

preload fetches one specific resource at high priority during the initial page load, for example the LCP image or a blocking font. prefetch fetches a resource at low priority because it is needed on the next likely navigation. preconnect opens DNS, TCP, and TLS to an origin before any request is made, so a later request to that origin skips the handshake cost. dns-prefetch only resolves the hostname and is cheaper when the TLS warm-up is not worth it.

Why do fonts need crossorigin on preload?

Browsers fetch font files in CORS mode even when they come from the same origin. A preload tag without crossorigin triggers a second, non-CORS fetch that is discarded, so the font is downloaded twice and the preload warning appears in devtools. Always pair font preloads with crossorigin="anonymous".

Should I preload my LCP image?

Yes, when the image is discovered late by CSS or JavaScript and shows up in the Largest Contentful Paint element. Place the preload tag early in the head and set as="image". Preloading an image that is already in the initial HTML img tag with fetchpriority="high" is redundant and can compete for bandwidth.

How many preconnect origins should a page use?

Keep it to around four origins that actually serve critical resources — typically the CDN for fonts or images, and one API origin if the LCP depends on it. Each preconnect costs DNS, TCP, and TLS work even if the request never happens, so preconnecting analytics or ad domains on the critical path slows the page down.

Can resource hints be sent as an HTTP Link header?

Yes. nginx, CDNs, and some application servers can emit Link: <url>; rel=preload; as=style headers, which the browser processes before the HTML arrives. The generator produces both the HTML <link> form and the Link header form so you can pick the one your stack supports, or use the header for early hints at the edge.

Does modulepreload replace a regular script tag?

No. modulepreload tells the browser to fetch an ES module and its dependency graph at high priority, but the module still needs a script type="module" tag (or a runtime import() call) to execute. Use modulepreload for entry modules that would otherwise be discovered after the first JavaScript chunk parses.

Do the generated tags send any data off my machine?

No. The generator renders tags and headers locally. The href values you type never leave the browser tab, and no analytics or network calls run in the tool path.