Asset Monitoring
Broken Assets Monitoring
A broken JavaScript bundle silently kills your checkout. A missing stylesheet makes your site look like it is from 1998. Your server still returns 200 OK the whole time. Sitewatch parses every page, checks every script, stylesheet, and image, and alerts you before your customers notice.
- Detect broken JavaScript and CSS bundles after deployments
- Catch missing images that erode trust and credibility
- Spot CDN failures and third-party script outages
Broken asset detected
Confirmed via 2-of-3 retries
Affected assets
Recent activity
- main.a4f2c.js -- 404 Not Found6:00 AM
- vendor.css -- MIME type text/html (expected text/css)6:00 AM
- hero-bg.webp -- 200 OK6:00 AM
- Inter-Regular.woff2 -- 200 OK6:00 AM
Why it matters
Your site is "up" but broken. That is the expensive kind of failure.
JavaScript failures
A missing JS bundle breaks form submissions, shopping carts, and checkout flows -- while your server happily returns 200 OK. Uptime tools see nothing wrong.
CSS breakage
A stylesheet returning a 404 or the wrong MIME type leaves users staring at raw, unstyled HTML. It looks like your site is from another decade.
Broken images
Missing product images, broken hero banners, and placeholder icons destroy credibility. Visitors who see broken images rarely come back.
CDN delivery failures
Your CDN returns an error page instead of your JavaScript bundle. The HTTP status might even be 200. Sitewatch catches it by validating the MIME type of every response.
Third-party failures
Payment scripts, analytics tags, and chat widgets can vanish or start returning errors. Your site still loads but critical features silently stop working.
SEO impact
Search engines penalize pages with missing resources. Every broken asset on a landing page is ad spend wasted and organic traffic lost.
3
Asset types checked (JS, CSS, images)
2-of-3
Retry confirmation
5–30 min
Check intervals
What gets flagged
Every asset referenced in your HTML, verified
Status and availability
- 404 and 410 errors on JavaScript and CSS bundles
- 5xx server errors on asset URLs
- Missing images, icons, and media resources
- Third-party scripts returning error status codes
MIME type and delivery
- JavaScript served as text/html (browsers refuse to execute it)
- CSS delivered with incorrect content-type headers
- CDN edge nodes returning error pages instead of assets
- Assets redirecting to unexpected URLs or error pages
How it works
How Sitewatch finds broken assets
Fetch your page
Sitewatch fetches the page over HTTP and parses the HTML to extract every referenced script, stylesheet, and image URL.
Check every asset
Each discovered asset gets a HEAD request to verify its HTTP status code and MIME type. A 200 with the wrong content-type is still a failure.
Confirm with retries
Detected issues go through 2-of-3 retry confirmation. Only persistent failures create an incident -- no noise from transient glitches.
Alert with evidence
Confirmed incidents trigger alerts across your configured channels with the exact asset URL, HTTP status code, failure type, and which page is affected.
How much revenue are broken assets costing you right now?
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The gap in your monitoring
Uptime tools miss the "up but broken" problem
| Feature | Uptime tools | Sitewatch |
|---|---|---|
| Broken JS bundles | Invisible -- server returns 200 | Every script checked for status + MIME type |
| Missing CSS | Not checked | Detected and reported with asset URL |
| CDN serving errors | Looks fine from ping | MIME type mismatch caught per asset |
| Third-party outages | Users discover it | Every referenced script verified |
| Alert evidence | Up/down only | Asset URL, status code, failure type |
| False positive prevention | Single check | 2-of-3 retry confirmation |
Broken JS bundles
Missing CSS
CDN serving errors
Third-party outages
Alert evidence
False positive prevention
FAQ
Frequently asked questions
Sitewatch checks every script, stylesheet, and image referenced in your page HTML. Each asset gets a HEAD request to verify its HTTP status code and MIME type. If an asset returns a 404, 5xx, or the wrong content-type, it is flagged as an incident.
Sitewatch fetches your page, parses the HTML to find all referenced assets, then sends a HEAD request to each one. It checks two things: the HTTP status code (is the asset actually there?) and the MIME type (is the server returning the right kind of file?). Issues are confirmed with 2-of-3 retries before creating an incident.
Yes. When a CDN serves an error page or returns the wrong MIME type for an asset, Sitewatch catches it. This is one of the most common "up but broken" failures -- the CDN returns 200 OK but the content-type is text/html instead of application/javascript, so browsers refuse to execute the script.
Check frequency is configurable per site. Free plans run checks every 30 minutes; Pro plans go as low as every 5 minutes. You can also trigger on-demand checks from the dashboard or via deploy hooks for instant post-deploy verification.
Yes. Sitewatch checks every script referenced in your page HTML, including third-party scripts from payment providers, analytics platforms, chat widgets, and ad networks. If any of them stop loading or return errors, you get an alert.
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