The fast, global infrastructure that powers unpkg is generously donated by [Cloudflare](https://www.cloudflare.com) and [Heroku](https://www.heroku.com).
The CDN caches all files based on their permanent URL, which includes the npm package version. This works because npm does not allow package authors to overwrite a package that has already been published with a different one at the same version number.
URLs that do not specify a package version number redirect to one that does. This is the `latest` version when no version is specified, or the `maxSatisfying` version when a [semver version](https://github.com/npm/node-semver) is given. Redirects are cached for 5 minutes.
Browsers are instructed (via the `Cache-Control` header) to cache assets for 4 hours.
I do my best to keep it running, but sometimes things go wrong. Sometimes there are network or provider issues outside my control. Sometimes abusive traffic temporarily affects response times. Sometimes I break things by doing something dumb, but I try not to.
The goal of unpkg is to provide a hassle-free CDN for npm package authors. It's also a great resource for people creating demos and instructional material. However, if you rely on it to serve files that are crucial to your business, you should probably pay for a host with well-supported infrastructure and uptime guarantees.
