Third-Party Resource Checker
See every external resource your website loads — scripts, fonts, CDNs, stylesheets, and images. Find broken dependencies before your users do.
Free tool · No signup required · Instant scan results
What This Tool Scans
What Are Third-Party Resources on a Website?
Third-party resources are files your website loads from external servers — domains you don't control. Every time a visitor opens your page, their browser fetches these resources alongside your own content.
Common types include JavaScript libraries from CDNs (jQuery, Bootstrap, React), web fonts from Google Fonts or Adobe, analytics scripts like Google Analytics or Hotjar, stylesheets from CSS frameworks, and images served from external image CDNs or social media embeds.
While third-party resources add functionality without extra development, each one creates a dependency on an external service. If that service goes down, slows down, or gets compromised, your website suffers — even if your own server is perfectly healthy.
How to Check What External Scripts a Website Loads
Method 1: Browser DevTools — Open Chrome DevTools (F12), go to the Network tab, reload the page, and filter by "third-party" requests. This works but requires manual analysis: you need to identify which domains are external, categorize resources by type, and check each one for errors.
Method 2: Use this tool — Enter your URL above and click "Scan." In seconds you get a categorized breakdown of every external resource, with failed and slow resources highlighted automatically. No DevTools expertise needed.
The scanner checks each resource's HTTP status code and load time, groups them by type (scripts, fonts, styles, images), and flags anything that failed to load or is unusually slow.
Why Third-Party Scripts Slow Down Your Website
Every third-party resource adds overhead: DNS lookup, TCP connection, TLS handshake, and data transfer. Render-blocking scripts in the <head> delay your page from displaying anything until they finish loading.
Third-party code is responsible for a significant portion of main-thread blocking time on most websites. This directly impacts Core Web Vitals — particularly Largest Contentful Paint (LCP) and Interaction to Next Paint (INP) — which Google uses as ranking signals.
The median website loads resources from around 12 third-party domains. Each additional domain requires a separate DNS resolution and connection setup, compounding the performance cost. Auditing your third-party resources and removing unnecessary ones is one of the highest-impact performance optimizations you can make.
Common External Dependencies and Their Risks
| Resource | Type | Risk |
|---|---|---|
| Google Fonts | Font | Render-blocking if not preloaded; layout shift on slow connections |
| jQuery CDN | Script | Entire page functionality breaks if CDN is unreachable |
| Google Analytics | Script | Blocks rendering if loaded synchronously; privacy regulations |
| Chat widgets | Script + Style | Heavy payload; often loads additional sub-dependencies |
| Bootstrap CDN | Style + Script | Unstyled content flash if CSS fails to load |
| Payment processors | Script | Checkout completely broken if script fails; high business impact |
How to Find Broken External Resources
Broken external resources are dependencies that return error status codes (4xx, 5xx) or fail to load entirely. They cause visible problems: missing fonts make text invisible or fall back to system fonts, failed scripts break interactive features, and missing stylesheets leave pages unstyled.
Our scanner automatically detects failed resources and shows them at the top of your results with the specific error code. Common causes include expired CDN URLs, deprecated library versions that have been removed, domain changes by the resource provider, or rate limiting on free CDN tiers.
Fix broken resources by self-hosting critical dependencies, updating to current CDN URLs, or removing resources your site no longer needs. For continuous monitoring, set up alerts that notify you the moment any dependency starts failing.
Third-Party CDN Checker — Which CDNs Does a Website Use?
CDNs (Content Delivery Networks) host and distribute resources like JavaScript libraries, CSS frameworks, and fonts from edge servers worldwide. Popular CDNs include jsDelivr, cdnjs, unpkg, Google Hosted Libraries, and Cloudflare's CDNJS.
Use the scanner above to identify which CDNs your website relies on. The results show the full URL of each resource, making it easy to see which CDN provider serves each dependency. This is valuable for security audits (knowing your supply chain), performance optimization (consolidating CDN providers), and incident response (quickly identifying if a CDN outage affects your site).
If you depend on a single CDN for multiple critical resources, consider adding fallback URLs or self-hosting the most important assets. A CDN outage shouldn't take your entire website down.