Monitoring

    Cache-Control header check

    Grades your Cache-Control headers on static assets, HTML, and API responses — bad caching is a leading hidden cause of slow LCP.

    Updated 2026-07-10
    1 min read
    cache-control
    caching
    performance

    Quick answer#

    Lemwatch samples 20 assets per page load and grades Cache-Control against Google's recommendations.

    What it checks#

  1. Static assets: max-age ≥ 1 year + immutable
  2. HTML: no-cache or short max-age
  3. API JSON: private + short max-age
  4. Missing Cache-Control (worst case) flagged

    5. Where to find it in Lemwatch#

    Site details → Performance → Caching.

    How to fix#

  5. Fingerprint asset filenames (app.abc123.js).
  6. Serve fingerprinted assets with Cache-Control: public, max-age=31536000, immutable.
  7. HTML gets Cache-Control: no-cache so users see deploys immediately.
  8. Re-run.

    9. FAQ#

    Is immutable safe?#

    Yes — as long as filenames change on every deploy.

    What about ETag?#

    Still useful, but Cache-Control is the primary signal.

    Related#

  9. Performance budgets
  10. Gzip/Brotli compression check
  11. Core Web Vitals
    12. Was this article helpful?

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