jsDelivr

What Is jsDelivr?

jsDelivr is a free, open-source public content delivery network (CDN) that serves JavaScript libraries, CSS, fonts, and other static assets directly from package registries such as npm and from public GitHub repositories. The short answer for anyone asking what jsDelivr is: it is one of the most widely used free CDNs on the web, letting any website load popular libraries from a fast, globally distributed network by simply pointing a <script> or <link> tag at a cdn.jsdelivr.net URL, without hosting the files itself.

jsDelivr was created by Dmitriy Akulov and has grown into a community-backed project supported by multiple infrastructure providers. Rather than running its own single network, jsDelivr operates as a multi-CDN, intelligently routing each request across the networks of several partners (historically including Cloudflare, Fastly, and Bunny) to maximize uptime and speed. This means that even if one underlying provider has an outage in a region, requests can be served from another, giving jsDelivr unusually strong reliability for a free service.

A precise, current market-share figure is difficult to state with confidence because CDN usage is measured differently across detection surveys, and many sites load assets from several CDNs at once. What technology-detection sources such as Wappalyzer and BuiltWith consistently report, however, is that jsDelivr is among the most commonly detected public CDNs on the web, especially on WordPress sites, open-source project pages, documentation sites, and smaller independent websites that want library hosting without operating their own infrastructure. Its tight integration with npm and GitHub is the main reason it became a default choice: any package published to npm or any file in a public GitHub repository becomes instantly available through a jsDelivr URL.

How jsDelivr Works

jsDelivr works by acting as a caching proxy in front of public package sources. When a browser requests a file from a cdn.jsdelivr.net URL, jsDelivr resolves that URL to a specific file in npm, GitHub, or another supported source, fetches and caches it at edge locations around the world, and serves it to the visitor from the nearest point of presence. Subsequent requests for the same file are served straight from cache, so the original source is rarely hit.

The URL structure is the key to understanding how jsDelivr is used and detected. It follows predictable patterns based on the source:

• npm packages use the /npm/ path: https://cdn.jsdelivr.net/npm/package@version/file. For example, https://cdn.jsdelivr.net/npm/[email protected]/dist/jquery.min.js.
• GitHub files use the /gh/ path: https://cdn.jsdelivr.net/gh/user/repo@version/file. For example, https://cdn.jsdelivr.net/gh/twbs/[email protected]/dist/css/bootstrap.min.css.
• WordPress plugins and themes are also mirrored through a dedicated /wp/ path.

Version handling is one of jsDelivr's most useful behaviors. You can pin an exact version (@3.7.1) for maximum stability, request the latest patch of a major version (@3), or omit the version entirely to receive the newest release. jsDelivr also offers combined requests, where multiple files are bundled into a single response using a combine URL, reducing the number of round trips a browser must make.

Behind the scenes, jsDelivr applies automatic optimizations. It minifies eligible files on the fly, serves modern compression such as Brotli and gzip, sets aggressive long-lived cache headers, and supports modern transport protocols including HTTP/2 and HTTP/3. Because the same file requested by many different websites is cached under the same URL, popular libraries are almost always served from a warm edge cache, which is why load times are typically very fast.

A typical request lifecycle looks like this: a visitor's browser encounters a <script src="https://cdn.jsdelivr.net/npm/..."> tag, performs a DNS lookup for cdn.jsdelivr.net, connects to the nearest edge node selected by the multi-CDN routing layer, and receives the cached, compressed file with caching headers that let the browser reuse it on future visits.

How to Tell if a Website Uses jsDelivr

jsDelivr leaves clear, easy-to-spot fingerprints because its asset URLs are visible directly in a page's HTML. Here are the signals to look for and the tools that surface them.

Signals in the page and network

• Asset domain. The single clearest signal is the presence of cdn.jsdelivr.net in <script src="..."> or <link href="..."> tags. Any reference to this domain means the page is loading at least one asset through jsDelivr.
• /npm/ and /gh/ path patterns. jsDelivr URLs almost always contain /npm/ (for npm packages) or /gh/ (for GitHub files), frequently with a version pinned via @version and ending in a minified file such as .min.js or .min.css.
• Combined-file URLs. A URL containing /combine/ indicates jsDelivr's bundling feature, where several files are merged into one request.
• Response headers. A request to a jsDelivr asset typically returns CDN headers. Look for headers indicating the serving CDN, long cache-control max-age values, and x-served-by or similar caching markers in the network response.
• WordPress association. On WordPress sites, jsDelivr is often used by plugins or themes to offload library hosting, so seeing cdn.jsdelivr.net alongside /wp-content/ paths is common.

Tools to confirm it

Tool	What you do	What it reveals
View Source	Open the page source in your browser	cdn.jsdelivr.net script and link tags with /npm/ or /gh/ paths
DevTools Network	Open DevTools, reload, and filter requests by jsdelivr	Every asset loaded from jsDelivr, with full URLs and response headers
curl -I	Run curl -I https://cdn.jsdelivr.net/npm/[email protected]/dist/jquery.min.js	Response headers showing caching behavior and the serving CDN
Wappalyzer	Run the browser extension on the page	Flags jsDelivr in the CDN category
BuiltWith	Enter the domain on the BuiltWith site	Reports current and historical jsDelivr detection

Identifying the CDN a site uses is often the first step in mapping its wider stack. For a broader walkthrough, see our guide on how to check what JavaScript libraries a website uses, the primer on what a CDN is and whether you need one, and the general overview of how to find out what technology a website uses. A jsDelivr URL frequently reveals the exact library and version a site loads, which makes it a useful anchor for the rest of your investigation.

Key Features

jsDelivr's feature set is built around being free, fast, and effortless to use while remaining reliable enough for production traffic.

• Free and open source. There is no cost, no account requirement, and no usage cap for normal traffic, which is why it is so widely adopted.
• npm and GitHub integration. Any public npm package or GitHub file is instantly available through a jsDelivr URL, with no manual upload step.
• Multi-CDN reliability. Requests are load-balanced across multiple underlying CDN providers, so an outage at one provider does not take jsDelivr offline.
• Flexible version pinning. Pin an exact version, a major version range, or always-latest, giving control over the stability-versus-freshness trade-off.
• Automatic optimization. On-the-fly minification, Brotli/gzip compression, and long cache lifetimes are applied without configuration.
• File combining. Multiple files can be merged into a single request to reduce round trips.
• Global edge network. Hundreds of points of presence worldwide keep latency low for international visitors.

A few of these deserve emphasis. The multi-CDN architecture is jsDelivr's defining technical feature and the main reason it can offer enterprise-grade uptime for free; very few public CDNs spread load across several networks this way. The GitHub /gh/ support is also distinctive, because it lets developers serve files straight from a repository without publishing to npm at all, which is popular for small scripts, demos, and project assets. And the always-warm cache for popular libraries means commonly used files like jQuery or Bootstrap are almost never fetched cold, delivering consistently fast performance.

Pros and Cons

jsDelivr's trade-offs flow from its nature as a free, shared, third-party public CDN.

Pros

• Completely free with no account or configuration required.
• Excellent uptime thanks to multi-CDN load balancing across several providers.
• Instant access to the entire npm registry and any public GitHub repository.
• Fast global delivery with modern compression and protocol support.
• Flexible versioning and file-combining features that fine-tune performance.
• Reduces load and bandwidth costs on the site's own origin server.

Cons

• Adds a third-party dependency; if jsDelivr were ever unreachable, affected assets would fail to load unless a fallback exists.
• Loading scripts from an external domain introduces a supply-chain consideration, which is why pairing jsDelivr URLs with Subresource Integrity (SRI) hashes is recommended.
• An extra DNS lookup and connection to a new domain can add a small amount of latency for a visitor's very first request.
• Less control than self-hosting; the site owner does not govern the serving infrastructure directly.
• Privacy-conscious projects may prefer first-party hosting to avoid any third-party request.

jsDelivr vs Alternatives

jsDelivr competes with other public CDNs that serve open-source libraries. The comparison below frames where it sits relative to the most common alternatives.

CDN	Primary sources	Distinctive trait	Best for
jsDelivr	npm, GitHub, WordPress	Multi-CDN load balancing, file combining	Reliable free hosting for npm/GitHub assets
unpkg	npm	Simple, direct npm file mirror	Quick loading of any npm package
cdnjs	Curated open-source libraries	Hand-curated, vetted library list	Trusted, well-known libraries only
Google Hosted Libraries	A small fixed set of major libraries	Backed by Google's network	jQuery and a few classic libraries

The most instructive comparison is jsDelivr versus unpkg. Both serve npm packages through clean, predictable URLs, and both are popular choices for loading libraries without self-hosting. The practical differences are that jsDelivr also serves files directly from GitHub via its /gh/ path, offers automatic file combining, and runs as a multi-CDN for redundancy, whereas unpkg focuses tightly on being a fast, no-frills mirror of npm. For projects that only need npm packages and value simplicity, unpkg is often sufficient; for projects that want GitHub hosting, bundling, or the extra reliability of multi-CDN routing, jsDelivr tends to be the stronger pick. Compared with curated CDNs, jsDelivr's advantage is breadth (the whole of npm and GitHub) at the cost of the human vetting that a curated list provides.

Use Cases

jsDelivr fits a recognizable set of scenarios where a site needs reliable, free hosting for static assets.

• Loading popular libraries. Serving jQuery, Bootstrap, Vue, Chart.js, and similar libraries from a fast CDN without bundling them into the site's own assets.
• WordPress and plugin asset hosting. Plugins and themes frequently offload their JavaScript and CSS to jsDelivr to reduce origin load.
• Open-source project pages and docs. Documentation sites and demos load examples and dependencies straight from npm or GitHub through jsDelivr URLs.
• Serving files from a GitHub repo. Developers use the /gh/ path to deliver small scripts, configuration files, or assets directly from a repository without publishing a package.
• Prototyping and quick experiments. Dropping a single <script> tag into a page to try a library instantly, with no build step.

For competitive research and lead generation, spotting jsDelivr on a prospect's site reveals which libraries and versions they depend on, since the exact package and version are usually embedded right in the URL. That is a valuable signal when profiling a site's front-end stack and its maintenance habits.

Frequently Asked Questions

Is jsDelivr free to use?

Yes. jsDelivr is a free, open-source public CDN with no account requirement and no usage cap for normal website traffic. It is funded by sponsorships and infrastructure partners rather than by charging end users, which is part of why it is so widely adopted across personal sites, open-source projects, and WordPress installs.

How can I tell which library and version a jsDelivr URL is serving?

Read the URL directly. A jsDelivr asset URL embeds the source and version: cdn.jsdelivr.net/npm/[email protected]/dist/jquery.min.js tells you it is jQuery version 3.7.1 from npm, while a /gh/user/repo@tag/ path tells you the exact GitHub repository and tag. Open the Network tab in DevTools or View Source to read the full URLs.

Is jsDelivr safe and reliable for production?

jsDelivr is widely used in production and is unusually reliable for a free service because it load-balances across multiple underlying CDN providers, so a single provider's outage does not take it down. For added safety against tampering, many sites pair jsDelivr URLs with Subresource Integrity (SRI) hashes so the browser verifies the file's contents before executing it.

What is the difference between the /npm/ and /gh/ paths?

The /npm/ path serves files from packages published to the npm registry, while the /gh/ path serves files directly from public GitHub repositories. The /npm/ path is the most common and is used for established libraries; the /gh/ path is handy for delivering scripts or assets that live in a repository but were never published as an npm package.

Does using jsDelivr slow down or speed up my site?

For most sites it speeds things up. Popular libraries are served from edge caches close to the visitor, with modern compression and long cache lifetimes, and the file is often already cached in the browser from another site that uses the same URL. The only minor cost is an extra DNS lookup and connection to the jsDelivr domain on a visitor's first request.

Want to identify the CDNs, libraries, and full technology stack behind any website instantly? Try StackOptic at https://stackoptic.com.