What is a MIME type mismatch and why does it matter?

A MIME type mismatch occurs when a CDN or server serves a file with the wrong content-type header -- for example, serving JavaScript as text/html. Modern browsers enforce strict MIME checking and will refuse to execute scripts with incorrect types, silently breaking your page while your server logs show 200 OK.

How does Sitewatch detect CDN failures?

Sitewatch fetches your page and parses the HTML to find every referenced asset. Each asset gets a HEAD request to check its HTTP status code and MIME type. If a CDN serves an error, the wrong content type, or a 404, the failure is caught and reported with the exact asset URL and failure details.

Does Sitewatch compare asset content hashes?

No. Sitewatch checks the HTTP status code and MIME type of each asset, not the content itself. This catches the most common CDN failures: assets returning errors, wrong content types, or 404s after cache invalidation. It does not track asset versions or compare file contents between checks.

What CDN providers does Sitewatch work with?

Sitewatch works with any CDN -- Cloudflare, AWS CloudFront, Fastly, Akamai, Vercel Edge, and others. It monitors what gets delivered to the browser rather than relying on CDN-specific APIs, so it works regardless of your infrastructure.

How often are checks run?

Checks run on a configurable schedule -- every 30 minutes on Free, down to every 5 minutes on Pro. You can also trigger a check on demand from the dashboard or via deploy hooks, ideal for verifying a CDN cache invalidation worked correctly.

CDN monitoring

CDN & Cache Issues Detection

Your CDN returns 200 OK. But the response body is an HTML error page, not your JavaScript bundle. The browser refuses to execute it. Your checkout breaks. Your uptime tool sees nothing wrong. Sitewatch checks the actual HTTP status and MIME type of every asset on your pages -- so CDN failures get caught, not hidden.

Detect when CDN edge nodes serve errors instead of your assets
Catch MIME type mismatches that silently break browsers
Flag missing or erroring assets on CDN-served URLs

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Incident detected

Medium

CDN delivery failure detected

Confirmed via 2-of-3 retries

Affected resources

Recent activity

app.js -- MIME type text/html (expected application/javascript)6:00 AM
vendor.css -- 404 Not Found6:00 AM
hero-image.webp -- 200 OK6:00 AM
fonts/Inter.woff2 -- 200 OK, correct MIME type6:00 AM

Why it matters

CDN failures are invisible to your server and devastating to your visitors

CDN delivery failures

A CDN edge node returns an error page instead of your JS bundle. The status code is 200. Your server logs look clean. But the browser sees text/html where it expected application/javascript and refuses to execute it. Your site breaks.

MIME type mismatches

Modern browsers enforce strict MIME checking. If a CDN serves JavaScript with a text/html content type, the script is silently blocked. No console error for most users. Just a broken page.

Missing assets on CDN

A deploy invalidates CDN cache but the new files are not there yet. Or a CDN region is out of sync. Assets return 404 while your origin server has them. Sitewatch checks from the outside, like your visitors.

Wrong content types

CDN misconfigurations can serve CSS as application/octet-stream, images with wrong headers, or scripts as plain text. Browsers handle each case differently, but the result is always broken functionality.

Asset redirects and chains

CDN routing rules can redirect asset URLs to error pages, login screens, or entirely different files. Sitewatch follows redirects and validates what actually gets served.

The "up but broken" gap

Your origin returns 200. Your CDN returns 200. But the content delivered to the browser is wrong. This is the gap between "up" and "working" that traditional monitoring ignores.

Incident types detected

2-of-3

Retry confirmation

5–30 min

Check intervals

What gets flagged

CDN and delivery issues Sitewatch catches

MIME type and content failures

JavaScript served as text/html -- browsers block execution
CSS delivered with wrong content-type headers
Assets served with unexpected MIME types after CDN routing
Non-HTML content returned for pages that should be HTML

Status code and availability

404 and 410 errors on CDN-served asset URLs
5xx errors from CDN edge nodes
Asset URLs redirecting to error pages or wrong destinations
Missing assets after CDN cache invalidation or deploy

How it works

How Sitewatch detects CDN issues

Fetch your page

Sitewatch fetches the page over HTTP from outside your infrastructure and parses the HTML to extract every referenced script, stylesheet, and image URL.

Check every asset

Each asset gets a HEAD request to verify its HTTP status code and MIME type. This catches CDN edge nodes returning errors, wrong content types, or redirects.

Confirm with retries

Detected issues go through 2-of-3 retry confirmation. Transient CDN glitches are filtered out. Only persistent failures create incidents.

Alert with context

Confirmed failures trigger alerts across your configured channels with the asset URL, HTTP status code, expected vs. actual MIME type, and which page is affected.

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The monitoring gap

Your CDN dashboard says healthy. Your visitors say broken.

Feature	Basic monitoring	Sitewatch
MIME type validation	Not checked	Every asset verified
CDN error detection	Origin returns 200, looks fine	Checks what CDN actually delivers
Asset status codes	Only page-level ping	Every JS, CSS, and image checked
Redirect detection	Not checked	Asset redirect chains caught
False positive prevention	Single check	2-of-3 retry confirmation
Post-deploy verification	Manual browser check	Automatic on next check cycle

MIME type validation

Basic monitoring:Not checked

Sitewatch:Every asset verified

CDN error detection

Basic monitoring:Origin returns 200, looks fine

Sitewatch:Checks what CDN actually delivers

Asset status codes

Basic monitoring:Only page-level ping

Sitewatch:Every JS, CSS, and image checked

Redirect detection

Basic monitoring:Not checked

Sitewatch:Asset redirect chains caught

False positive prevention

Basic monitoring:Single check

Sitewatch:2-of-3 retry confirmation

Post-deploy verification

Basic monitoring:Manual browser check

Sitewatch:Automatic on next check cycle

FAQ