For developers · REST API

The WebP conversion API for your backend, CMS and CI

Everything the browser converter does, as one HTTPS request. Send an image with a quality value and a maximum width, receive an optimised WebP. Built for upload hooks, build pipelines and media libraries with thousands of images.

Get API access Read the request format

$99/month·Key emailed after payment·Cancel anytime

API plan

For developers

$99/ month

Server-side conversion over HTTPS. Your API key is emailed right after payment.

REST endpoint: send an image, get WebP back
Same quality and max-width controls as the app
50,000 conversions per month, 60 requests per minute
Images up to 25 MB, processed and discarded immediately
Works from any language, CI pipeline or CMS hook
Priority support with a developer on the other end

Billed monthly, cancel anytime. 14-day money-back guarantee.

How it works

Three steps from checkout to your first WebP

Step 1

Subscribe and receive your key

Pay through Stripe. Your API key lands in your inbox within minutes, no dashboard or account setup required.

Step 2

Send an image

One multipart POST with the file, a quality value and an optional maximum width. Any language that can make an HTTP request works.

Step 3

Get WebP back

The response body is the converted image, ready to write to disk or stream to your CDN. Size and dimensions come back as headers.

Reference

The request

A single endpoint. Authenticate with your key, send the image as multipart form data, tune the output with two parameters.

POSThttps://api.fastwebpconverter.com/v1/convert

Header Authorization: Bearer YOUR_API_KEY · Body multipart/form-data · Response image/webp

convert.sh — bash
curl -X POST https://api.fastwebpconverter.com/v1/convert \
  -H "Authorization: Bearer $FASTWEBP_API_KEY" \
  -F "file=@./hero.png" \
  -F "quality=80" \
  -F "max_width=1600" \
  --output hero.webp

Parameters

Field	Type	Required	Description
file	multipart file	Yes	The source image: PNG, JPG, GIF, BMP, AVIF, SVG or HEIC. Up to 25 MB.
quality	integer 1–100	No (default 80)	WebP compression quality. 75–85 is ideal for photos; 90+ for UI screenshots and text.
max_width	integer (px)	No	Maximum output width. Larger images are downscaled with the aspect ratio preserved; smaller images are never upscaled.

Reference

The response

On success the body is the WebP binary and the interesting numbers travel in headers, so you can log savings without parsing anything.

Success · 200

Header	Example	Meaning
Content-Type	image/webp	The body is the converted image.
X-Original-Bytes	2493112	Size of the uploaded file.
X-Webp-Bytes	287401	Size of the WebP result.
X-Output-Width / X-Output-Height	1600 / 1067	Final dimensions after resizing.
X-RateLimit-Remaining	58	Requests left in the current minute.
X-Quota-Remaining	49877	Conversions left in the current billing month.

Errors

Status	Code	When
400	invalid_parameter	quality outside 1–100, max_width not a positive integer, or missing file.
401	unauthorized	Missing or invalid API key.
413	file_too_large	Upload exceeds 25 MB.
415	unsupported_format	The file is not a supported image type.
422	decode_failed	The image is corrupt or could not be decoded.
429	rate_limited	More than 60 requests per minute or monthly quota exhausted.

Errors return JSON with a stable code you can branch on:

400 Bad Request — json
{
  "error": {
    "code": "invalid_parameter",
    "message": "quality must be an integer between 1 and 100",
    "param": "quality"
  }
}

Use cases

Where a WebP API pays for itself

Anywhere images are uploaded by people who will not open a converter.

CMS upload hooks

Convert on upload in WordPress, Strapi, Sanity or a custom admin so editors never think about formats.

E-commerce catalogues

Normalise supplier photos to a fixed width and quality as they enter your product database.

Build pipelines

Run it in CI to convert assets committed as PNG so the deployed site only ships WebP.

User-generated content

Shrink avatars and post images before they hit your storage bucket and CDN bill.

API questions

Subscribe with the button on this page. Stripe processes the payment and we email your API key, together with a quick-start message, to the address you enter at checkout, usually within a few minutes.

Yes: unlike the browser converter, the API runs on our infrastructure so it works from any backend. Images are processed in memory and discarded immediately after the response is sent. Nothing is stored or logged beyond byte counts.

50,000 conversions per month, 60 requests per minute and 25 MB per image. Need more? Contact us for a custom tier.

PNG, JPEG, GIF (first frame), BMP, AVIF, SVG and HEIC, the same formats as the browser converter. Output is always WebP.

Yes. A key identifies your subscription, not a machine. Keep it in an environment variable or secret manager and never ship it to browsers.

Any time, from the Stripe customer portal link in your receipt. The key keeps working until the end of the paid month, and the 14-day money-back guarantee applies like on every plan.

Ready to automate your image pipeline?

$99/month. Your API key is emailed as soon as payment completes.

Get API access