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Skillsnetlify-image-cdn

netlify-image-cdn

Design & creation

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Updated 10-16 06:50

About this skill

Netlify Image CDN

Transform images by requesting the endpoint with a url query parameter. This is the current and only documented surface — there is no legacy form.

GET /.netlify/images?url=<source>[&w=][&h=][&fit=][&position=][&fm=][&q=]

# resize a deployed image to 50px wide
curl -vs 'https://mysitename.netlify.app/.netlify/images?url=/owl.jpeg&w=50'

url is required; all other parameters are optional.

Query parameters

Parameter Purpose Values Default
url Source asset (required) Relative path or remote URL —
w Width in pixels Integer —
h Height in pixels Integer —
fit Resize behavior contain, cover, fill contain
position Crop anchor when fit=cover top, bottom, left, right, center center
fm Output format avif, jpg, png, webp, gif, blurhash content-negotiated
q Quality for lossy output Integer 1–100 75

Common transformations

# resize + crop to a 50px square, retaining the left side
curl -vs 'https://mysitename.netlify.app/.netlify/images?url=/owl.jpeg&fit=cover&w=50&h=50&position=left'

# convert JPEG to PNG (response carries content-type: image/png)
curl -vs 'https://mysitename.netlify.app/.netlify/images?url=/owl.jpeg&fm=png'

# convert JPEG to AVIF at medium quality
curl -vs 'https://mysitename.netlify.app/.netlify/images?url=/owl.jpeg&fm=avif&q=50'

fit behavior

  • contain (default): maintains aspect ratio; one dimension may come back smaller than requested. Supply one dimension and the other is computed.
  • cover: fills exactly, cropping excess. Requires BOTH w and h — omitting either is invalid. Use position to choose what's retained.
  • fill: fills exactly, stretching/squishing if aspect ratios differ.

Format notes

  • q applies only when output is avif, jpg, gif, or webp.
  • webp and gif can be static or animated.
  • If fm is omitted, format is content-negotiated from the Accept header: webp if accepted, else avif if accepted, else the original format. A source-only request (no other params) still converts to webp/avif but keeps size and shape.

Remote source images

Remote sources must be allowlisted in netlify.toml before transformation, or the request fails.

[images]
  remote_images = ['https://my-images\.com/.*', 'https://animals.more-images.com/[bcr]at/.*']

Percent-encode remote source URLs before placing them in the url parameter with encodeURIComponent — a URL containing ? or & breaks otherwise.

const src = `/.netlify/images?url=${encodeURIComponent('https://my-images.com/owl.jpeg?v=2')}&w=400`;

Constraints:

  • Remote sources must be publicly accessible.
  • Credential-bearing headers (Authorization, Cookie) are NOT forwarded when fetching a remote source. For authenticated sources, use URLs that carry their own authorization (e.g. S3 presigned URLs) and make sure your remote_images patterns match those full URLs.

remote_images regex escaping

The only meaningful escape is the literal dot (\.). Forward slashes are NOT metacharacters — never write https:\/\/. In netlify.toml, use single-quoted literal strings ('https://example\.com/.*') or double the backslash in double-quoted strings ("https://example\\.com/.*"). A bare \. inside double quotes is invalid TOML.

Response codes

  • Invalid transformation parameter values → 404.
  • Valid new transformation → 200 with content and matching content-type.
  • Previously transformed (cached) image → 304.

Reusing parameters across images

Map a friendly path to the endpoint with a redirect/rewrite.

_redirects:

/transform-small/* /.netlify/images?url=/:splat&w=50&h=50 200

netlify.toml:

[[redirects]]
  from = "/transform-small/*"
  to = "/.netlify/images?url=/:splat&w=50&h=50"
  status = 200

Then GET /transform-small/owl.jpeg returns the transformed image. Cross-site redirects for transformations are NOT recommended — they can degrade site performance.

Caching headers

Apply custom headers to source images on the site's own domain; they carry through to the transformed output.

netlify.toml:

[[headers]]
  for = "/source-images/*"
  [headers.values]
    Cache-Control = "public, max-age=604800, must-revalidate"
  • Custom headers can be applied to source images on the site's domain only — NOT to remote source images (Netlify does respect cache headers the external domain sends).
  • Cache-Control on source images applies only to browsers and CDNs in front of Netlify, NOT the Netlify Cache itself.

Blur placeholders (fm=blurhash)

fm=blurhash returns a BlurHash text string, not image bytes. Pointing an <img src> (or CSS background) at it renders nothing. Fetch the string ahead of time, decode it client-side with a BlurHash library (https://blurha.sh), and load the real image as a separate request without fm=blurhash.

Local development

The /.netlify/images endpoint, [images] allowlisting, and image redirects only exist under netlify dev (Netlify CLI). A local 404 on /.netlify/images almost always means a framework dev server (vite, next dev, astro dev) is running instead of netlify dev — the URL itself is usually fine. Start the local environment with netlify dev.

User-uploaded image pipelines

For pipelines composing Functions + Blobs + Image CDN (handling user-uploaded images), see references/user-uploads.md.

Framework image handling

Many frameworks route their built-in image optimization through Netlify Image CDN — use the framework's standard image component/syntax and only configure the remote allowlist. For unlisted frameworks, call /.netlify/images directly.

Framework Prerequisites Remote allowlist location
Angular None; NgOptimizedImage uses it automatically [images] remote_images in netlify.toml
Astro None; <Image /> uses it automatically image.domains or image.remotePatterns in astro.config.mjs
Gatsby (both 5.13+ and 5.11 or earlier) Set env NETLIFY_IMAGE_CDN=true; use Contentful/Drupal/WordPress source plugins [images] remote_images in netlify.toml
Next.js Next.js 13.5+ and Next.js adapter v5 remotePatterns in next.config.js
Nuxt None; nuxt/image module uses it automatically image.domains in nuxt.config.ts

Setup guides: Angular, Astro, Gatsby, Next.js, Nuxt.

Additional constraints

  • Deploy behavior: transforms respect atomic deploys; changing a source image in a new deploy re-runs transforms on subsequent requests.
  • Split Testing is NOT supported — image results may be inconsistent across split test branches.
  • Netlify Image CDN is NOT part of Netlify's HIPAA-compliant hosting offering.

Interactive parameter playground: https://image-cdn-playground.netlify.app/

Netlify house rules (image-cdn)

These are org conventions, not docs facts — merged into the rendered skill by ctx-gen and never generated. Owned by the skills maintainer.

  1. For user-uploaded image pipelines (Functions + Blobs + Image CDN composed), see references/user-uploads.md in this skill — an authored guide with no single docs source.
  2. Percent-encode remote source URLs before placing them in the url parameter (encodeURIComponent) — URLs containing ? or & break otherwise.
  3. fm=blurhash returns a BlurHash TEXT string, not image bytes. Pointing an <img src> (or CSS background) at it renders nothing — fetch the string ahead of time, decode it client-side with a BlurHash library, and load the real image as a separate request without fm=blurhash.
  4. A local 404 on /.netlify/images almost always means a framework dev server (vite, next dev, astro dev) is running instead of netlify dev — the endpoint, [images] allowlisting, and image redirects only exist under netlify dev. The URL itself is usually fine.
  5. In remote_images patterns, the meaningful regex escape is the dot; forward slashes are not metacharacters — do not write https:\/\/. In netlify.toml, use a single-quoted literal string ('https://example\.com/.*') or double the backslash in a double-quoted string ("https://example\\.com/.*") — a bare \. inside double quotes is invalid TOML.