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Open Source Image CDN that provides image transformation API and supports the latest image formats, such as WebP, AVIF, Jpeg XL, and network client hints.

Table of Contents


We wrote a big blog on this, and here is TLDR:

Transformimgs is an image CDN for Web, so API must cover typical use cases, like thumbnails, zoom in product images, etc. Any new API endpoints must solve the above problems.

The goal is to have zero-config API that makes decisions based on the input, so you don't need to provide additional parameters like quality, output format, type of compression, etc.

Therefore, this allows you to configure the integration once. New features, like new image formats, will work with your front end automatically without any changes.

To achieve that goal we should keep API to bare minimum and hide the smartness in the implementation.


  • Resize/optimises/crops raster (PNG and JPEG) images.
  • JpegXL / AVIF / WebP support based on "Accept" header.
  • Vary header support - ready to deploy behind any CDN.
  • Responsive images support including high DPI (retina) displays
  • Save-Data support


There is an example of running API behind reverse proxy with integration example in quickstart/ folder.

To run:

cd quickstart
docker-compose up
open https://localhost


The API has 4 HTTP endpoints:

  • /img/{IMG_URL}/optimise - optimises image
  • /img/{IMG_URL}/resize - resizes image
  • /img/{IMG_URL}/fit - resize image to the exact size by resizing and cropping it
  • /img/{IMG_URL}/asis - returns original image


Running Locally


The latest docker image published on Docker hub

Starting the server:

$ docker run -p 8080:8080 pixboost/transformimgs [OPTIONS]

To verify:

  • Health check: curl http://localhost:8080/health
  • Transformation: open http://localhost:8080/img/


Everything below is optional and have sensible defaults.

Option Description Default
cache Number of seconds to cache image(0 to disable cache). Used in max-age HTTP response. 2592000 (30 days)
proc Number of images processors to run. Number of CPUs (cores)
disableSaveData If set to true then will disable Save-Data client hint. Should be disabled on CDNs that don't support Save-Data header in Vary. false

Running from source code


$ git clone
$ cd transformimgs
$ ./ 


We run SaaS version at with generous free tier.

Perks of SaaS version:

  • CDN with HTTP/3 support included
  • Dashboard with usage monitor
  • API Key support with domains allow list
  • AWS S3 integration
  • API workflows for cache busting and warmup
  • Version upgrades

Go modules have been introduced in v6.

Performance tests

There is a JMeter performance test you can run against a service. To run tests:

  • Start a performance test environment:
$ docker-compose -f docker-compose-perf.yml up
  • Run JMeter tests:
$ jmeter -n -t perf-test.jmx -l ./results.jmx -e -o ./results
  • Run JMeter WebP test:
$ jmeter -n -t perf-test-webp.jmx -l ./results-webp.jmx -e -o ./results-webp
  • Run JMeter AVIF test:
$ jmeter -n -t perf-test-avif.jmx -l ./results-avif.jmx -e -o ./results-avif
  • Run JMeter JPEG XL test:
$ jmeter -n -t perf-test-jxl.jmx -l ./results-jxl.jmx -e -o ./results-jxl

Opened tickets for images related features


Shout out with any ideas. PRs are more than welcome.




  • Add JpegXR support (IE supports WEBP)
  • Add Jpeg 2000 support (Safari support WEBP)
  • Client Hints - on hold due to browsers adoption
  • Save-Data header (Added in version 7.0.0)
  • SVG support
  • Consider using Zopfli or Brotli for PNGs
  • JpegXL Support since supported by Safari 17
  • GIF support (Added in version 6.1.0)