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Topic: CDN

Website: https://www.jsdelivr.com/

Type: service

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jsDelivr is a free CDN for open source files. We are tightly integrated with Github and npm allowing us to automatically provide a reliable CDN service to almost every open source project out there.

We offer a stable CDN that can be used in production on popular websites with huge amounts of traffic. There are no bandwidth limits or premium features and its completely free to use by anybody.

Ready for production

Our public CDN is built to be used in production by even the largest websites. Everything is optimized and being constantly improved to offer all users maximum speed and uptime. Performance is monitored at all times, and we are always looking into new technologies and providers that may further improve our CDN. Downtime, timeouts or slow responses are simply unacceptable.

We do everything possible to ensure our CDN will NEVER break any websites regardless of use-case. If a file is available via our CDN we assume its used in production and make sure that file will continue to work no matter what.

This includes dynamic endpoints such as /npm/, /gh/ and /combine/. When a file is first accessed it gets permanently stored in a reliable file system. This means that even if a npm package gets deleted, or an existing file gets removed by a developer, jsDelivr will continue to serve the stored copy for ever, without breaking any websites or causing any issues.

On top of that we also do version-fallback. This means that if a file used in version 1.0.1 is no longer available in 1.0.2 and a user requests the non-existant file we will fallback to the previous 1.0.1 version and serve it instead of failing with 404 error.


Unlike the competition, jsDelivr uses multiple CDN providers, resulting in the best possible uptime and performance. We currently use CloudFlare, and Fastly. In mainland China we use Quantil.

If a CDN goes down, websites that use jsDelivr won't have any issues because all traffic will be instantly redirected to remaining operational providers.
Smart Load Balancing

jsDelivr uses real user performance data (also known as RUM) to make its routing decisions. These metrics are gathered from hundreds of websites and are used in our load balancing algorithm to make accurate decisions for serving content.

All providers (CDNs and custom servers) are tested millions times per day by real users from all over the world. Based on this information, jsDelivr knows what provider is the fastest for each user. Each user gets a unique response based on his or her location, ISP, and the providers' uptime in real time.

This system also responds immediately to performance degradation and downtime of providers. If a CDN is under a DDoS attack, and their performance drops in some locations, in matter of seconds the algorithm will pick up the change and start serving a different provider to all affected users.


We have multiple layers of failover to protect our users from any downtime.

We use 2 DNS providers at the same time. For jsDelivr to go down both of these companies would have to go down at the same time.

Both of our DNS providers monitor our load-balanced endpoint and if they detect problems they will automatically switch all traffic to a single CDN provider.

Our load-balancer monitors the uptime of all CDN providers using both RUM and synthetic data. If any of those detect downtime or performance degradation that CDN provider will be removed immediately without any impact to our users.

Our origin consits of multiple servers in different data-centers. If a server goes down the CDNs will automatically switch to using the remaining healthy servers.

In total we have one of the most resilient systems out there, ready to be used in production by even the biggest companies.