Cache-Control for static files: Crawl Audit check 91

Short answer: the Cache-Control header tells a browser how long it may reuse a file without downloading it again. Static files, such as CSS, scripts, fonts and images, should be kept for a long time, so returning visitors and the next page load faster. Check 91 passes when a static file is cached for 30 days or more.

What Crawl Audit checks

• Full report: Crawl Audit requests one of your static files and reads its max-age. Pass at 30 days (2,592,000 seconds) or more; warning if shorter or missing.
• Free check: Crawl Audit reads the header on the HTML page itself and looks for a long max-age.

That free-check test has a flaw we've reported to the Crawl Audit team. HTML pages are usually, and rightly, set not to cache (max-age=0), so the free check can warn on a site whose static files are cached for a year. devmarde.com is one: our HTML has max-age=0, must-revalidate, and our CSS has public,max-age=31536000,immutable. Until it's fixed, trust the full report on this one.

What Google says

• Chrome's Lighthouse 13 guidance: "All cacheable subresource requests should have a cache lifetime of at least 30 days (2592000 seconds)." And: "cacheable resources should have a very long lifetime (30 days or 1 year)."
• The catch with long caching is that visitors might not see updates. The fix is "to embed a hash in your static asset filenames so that each version is unique".
• MDN: "When you use a cache-busting pattern for resources and apply them to a long max-age, you can also add immutable to avoid revalidation."

Cache-Control: public, max-age=31536000, immutable

On your platform

• Vercel and Next.js: hashed static files get max-age=31536000, immutable; Vercel notes "Frameworks like Next.js set this automatically."
• Shopify: "Shopify sets browser caching for cacheable resources to one year".
• Wix and Squarespace: caching of the platform's files isn't something you control.
• WordPress or your own server: a caching plugin, your host's panel, or nginx or Apache rules. Only cache for a year if file names change when the files do.

Sources

• Chrome for Developers, Use efficient cache lifetimes (8 October 2025) and Serve static assets with an efficient cache policy, checked 3 October 2026.
• MDN, Cache-Control.
• Vercel, Cache-Control headers; Shopify, Improving web performance.