Universal image CDN URL translator

There are many image CDNs that provide a URL API for transforming images. There is little consistency in these APIs, and it's often unclear what the API is for a given URL. This library aims to provide a consistent interface for detecting image CDN URLs and transforming them.

If you'd like to use this on the web, you might want to try Unpic img, a multi-framework image component, powered by Unpic.

It designed to work with image URLs from sources such as CMSs and other user-generated content, where the source image may or may not be from an image CDN, and may already have transforms applied. This allow different transforms to be applied for display on a website. A web framework may need to transform an image for display on a site. Rather than doing this by downloading and resizing it locally or re-processing it with a separate image service, this library can be used to transform the URL to use the original image CDN, which will then transform the image on the fly.

This library is available via NPM as unpic and JSR as @unpic/lib.

To use it in Node, install it from npm:

npm install unpic

Then import it in your code:

import { transformUrl } from "unpic";

To use it in Deno, import the module from JSR:

import { transformUrl } from "jsr:@unpic/lib";

If you previously installed the library from deno.land/x, you should update to use JSR instead as the deno.land/x version is no longer updated.

You can then use the transformUrl function to transform a URL:

const url = transformUrl(
	{
		url:
			"https://cdn.shopify.com/static/sample-images/bath_grande_crop_center.jpeg",
		width: 800,
		height: 600,
	},
);

console.log(url.toString());

// https://cdn.shopify.com/static/sample-images/bath.jpeg?width=800&height=600&crop=center

You can also use the parseUrl function to parse a URL and get the CDN and any params:

const parsedUrl = parseUrl(
	"https://cdn.shopify.com/static/sample-images/bath_800x600_crop_center.jpeg",
);

console.log(parsedUrl);
// {
//   cdn: "shopify",
//   width: 800,
//   height: 600,
//   base: "https://cdn.shopify.com/static/sample-images/bath.jpeg",
//   params: {
//     crop: "center",
//   },
// }

You can bypass auto-detection by specifying the CDN:

const url = transformUrl(
	{
		url:
			"https://cdn.shopify.com/static/sample-images/bath_grande_crop_center.jpeg",
		width: 800,
		height: 600,
		cdn: "shopify",
	},
);

This is particularly useful if you are using the CDN with a custom domain which is not auto-detected.

• Adobe Dynamic Media (Scene7)
• Builder.io
• Bunny.net, including caisy
• Cloudflare
• Contentful
• Contentstack
• Cloudinary
• Directus
• ImageEngine
• Imgix, including Unsplash, DatoCMS, Sanity and Prismic
• Kontent.ai
• Shopify
• Storyblok
• Vercel / Next.js
• WordPress.com and Jetpack Site Accelerator

Some transformers support URL delegation. This means that the source image URL is also checked, and if it matches a CDN then the transform is applied directly to the source image. For example: consider a next/image URL that points to an image on Shopify. The URL is detected as a nextjs URL because it starts with /_next/image. The nextjs transformer supports delegation, so the source image URL is then checked. As it matches a Shopify domain, the transform is applied directly to the Shopify URL. This means that the image is transformed on the fly by Shopify, rather than by Next.js. However if the source image is not a supported CDN, or is a local image then the nextjs transformer will return a /_next/image URL.

• What is an image CDN? An image CDN is a service that provides a URL API for transforming images. This is often used to resize images on the fly, but can also be used to apply other transforms such as cropping, rotation, compression, etc. This includes dedicated image CDNs such as Imgix and Cloudinary, CMSs such as Contentful, Builder.io and Sanity, general CDNs such as Bunny.net that provide an image API, but also other service providers such as Shopify. The CMSs and other service providers often use a dedicated image CDN to provide the image API, most commonly Imgix. In most cases they support the same API, but in others they may proxy the image through their own CDN, or use a different API.
• Why would I use this instead of the CDN's own SDK? If you you know that your images will all come from one CDN, then you probably should use the CDN's own SDK. This library is designed to work with images from multiple CDNs, and to work with images that may or may not be from a CDN. It is particularly useful for images that may come from an arbitrary source, such as a CMS. It is also useful for parsing URLs that may already have transforms applied, because most CDN SDKs will not parse these URLs correctly.
• Can you add support for CDN X? If it supports a URL API and doesn't require signed URLs then yes, please open an issue or PR.
• Can you add my domain to CDN X? If you provide a service where end-users use your URLs then probably. Examples may be image providers such as Unsplash, or CMSs. If it is just your own site then probably not. You can manually specify the CDN in the arguments to transformUrl and parseUrl.
• Can you support more params? We deliberately just support the most common params that are shared between all CDNs. If you need more params then you can use the CDN-specific API directly.
• Why do you set auto format? If the CDN support is, and no format is specified in transformUrl, the library will remove any format set in the source image, changing it to auto-format. In most cases, this is what you want. Almost all browsers now support modern formats such as WebP, and setting auto-format will allow the CDN to serve the best format for the browser. If you want to force a specific format, you can set it in transformUrl.
• Do you support SVG, animated GIF etc? If the CDN supports it, then yes. We don't attempt to check if a format is valid - we will just pass it through to the CDN. If the CDN doesn't support it, then it will return an error or a default.
• Do you support video, etc No, this library is only for images. If you pass a video URL to transformUrl, it will return undefined, as it will for any URL that is not recognised as an image CDN URL. It is up to you to handle this case.

See the contributing guide.