Cache Header Analyzer: Free Online Cache-Control Header Checker — How-To Guide

If a website feels slower than it should, or users keep seeing stale content after a deploy, the cause is often in the HTTP cache headers. The Cache Header Analyzer is a free online tool that inspects Cache-Control, ETag, and Vary headers and explains what they mean for browser and CDN caching — right in your browser, with nothing to install.

Try it free: Cache Header Analyzer

What the Tool Does

Paste real HTTP response headers into the tool and it runs parser and standards-based checks against them. It analyzes:

• Cache-Control — directives like max-age, no-cache, no-store, must-revalidate, and public/private, which decide whether browsers and CDNs can store a response and for how long.
• ETag — the validation token browsers send back on revalidation requests, so you can check whether your conditional-request strategy actually works.
• Vary — which request headers (like Accept-Encoding or Accept-Language) produce separate cached variants, and whether the variant count could hurt cache hit rates.

After running the checks, you review clear findings and can copy the output or download a text report for debugging notes, code review prep, or QA handoffs.

Step-by-Step: How to Use It

1. Collect your headers. Open your browser's DevTools, reload the page, and copy the raw Cache-Control, ETag, and Vary response headers. Or pull them with curl -I https://your-site.com/page and copy the header lines.
2. Open the tool. Go to the Cache Header Analyzer page.
3. Paste the headers. Drop the raw header text into the input box.
4. Run the checks. Trigger the parser and standards-based validation. The tool parses each header and flags issues — conflicting directives, missing revalidation signals, or Vary values that could fragment your cache.
5. Review the findings. Read through each finding. Common red flags include max-age=0 combined with missing ETag (no cheap revalidation path), or Vary: * (which effectively disables shared caching).
6. Copy or download the output. Export a text report to attach to a ticket or share with your team, then use Reset to clear the input before analyzing the next response.

Practical Tips

• Compare before and after a fix. Analyze the headers from the broken response, fix your server config, then analyze again. The side-by-side findings make it easy to confirm the change worked.
• Check assets vs. HTML separately. A good caching strategy looks different per resource type: long max-age with versioned filenames for static assets, and short or no-cache lifetimes for HTML. Run both through the analyzer to verify each does what you intend.
• Watch your Vary growth. Every value in Vary multiplies cache entries. If the analyzer shows a long Vary list on a high-traffic page, that's a strong hint to trim it down and improve CDN hit rates.

Frequently Asked Questions

Does the Cache Header Analyzer upload my headers?
No. The normal workflow runs locally in your browser — your input never leaves your device.

Is this a replacement for my CI or production scanner?
No. It is designed for fast local inspection before you run project-specific checks. For regulated production changes, always verify final results with your project's own compiler, CI checks, or infrastructure scanner.

Can I save the results?
Yes. Run the tool, then copy the output or download a text report — handy for debugging notes, QA handoffs, and documentation examples.

Do I need an account to use it?
No account is required. Just open the page, paste headers, and run the checks.

Privacy Note

The Cache Header Analyzer runs 100% in your browser. Your pasted headers and all analysis happen locally on your device — nothing is uploaded to a server.