For developers · REST API

The WebP conversion API for your backend, CMS and CI

Send an image, or its URL, with a quality and a maximum width; get an optimised WebP back, as bytes or as JSON with a download link. libwebp on our servers, animated GIFs stay animated, and the key is yours in a minute: create a free account and copy it from your account page.

Get a free API key Read the reference

Free: 50 conversions a monthSelf-serve keysOpenAPI 3.1

Quick start — bash
# Your key, from https://www.fastwebpconverter.com/account
export FASTWEBP_API_KEY=fwk_...
curl -X POST https://www.fastwebpconverter.com/api/v1/convert \
  -H "Authorization: Bearer $FASTWEBP_API_KEY" \
  -F "file=@photo.jpg" -F "quality=80" \
  -o photo.webp

Quick start

Your first WebP in three steps

Step 1

Create a free account

Sign in with a code sent to your e-mail or with Google. Every account, free included, comes with an API key and 50 conversions a month.

Step 2

Copy your key

On your account page, press Create key. It starts with fwk_ and is shown once: keep it in an environment variable such as FASTWEBP_API_KEY.

Step 3

Send an image

One POST with the file (or its URL) and the key as a Bearer token. The answer is the WebP itself, or JSON with a download link.

Create your account OpenAPI document

Reference

Endpoints and authentication

Two endpoints under one base URL. Authenticate every request with your key as a Bearer token; the same key also works for the MCP server.

Base URLhttps://www.fastwebpconverter.com/api/v1

HeaderAuthorization: Bearer fwk_...

POST/convertConvert one image to WebP

GET/usageYour plan and what is left this month

Spechttps://www.fastwebpconverter.com/openapi.json

CORS is open so you can test from a browser console, but keep keys on servers: anyone who sees a key can spend its allowance. Revoke a leaked key on your account page and create a new one.

POST /convert

Convert an image

JPG, PNG, GIF, WebP, AVIF, TIFF and SVG in, WebP out. Animated GIFs come out as animated WebP. HEIC photos and BMP files are not read on the server: the browser converter handles them (HEIC in Safari).

Three ways to send the image

Send the image as	Content-Type	Options in	Limit
An upload, field `file`	multipart/form-data	Form fields or query string	4 MB
A URL the server fetches	application/json	The JSON body or query string	10 MB on Free, 25 MB on Pro
The raw bytes as the body	image/* or application/octet-stream	Query string (?quality=80&filename=hero.png)	4 MB

Parameters

Parameter	Type	Default	Description
file	file (multipart)	—	The image. JPG, PNG, GIF, WebP, AVIF, TIFF and SVG.
url	string (http or https URL)	—	A public image URL. The server downloads it, checks it is an image and refuses private or local network addresses. Use it for images over the upload limit.
quality	integer 1–100	80	WebP quality. Ignored when lossless is true.
max_width	integer 16–10000 (px)	none	Downscale to this width, keeping the aspect ratio. Smaller images are never upscaled.
lossless	boolean	false	Lossless WebP: pixel-identical, best for logos, icons and flat graphics.
response	binary \| json	binary	json returns a JSON result with a download link instead of the bytes. Accept: application/json does the same.
filename	string (query)	image	Raw-body uploads only: the name the output is based on (hero.png gives hero.webp).

Upload a file, get the WebP back

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

Response headers

On success the body is the WebP and the numbers travel in headers, so you can log savings without parsing anything. They are exposed to browsers too.

Header	Example	Meaning
Content-Type	image/webp	The body is the converted image.
Content-Disposition	attachment; filename="hero.webp"	Output file name, from the source name.
X-Original-Bytes	2493112	Size of the source image.
X-Webp-Bytes	287401	Size of the WebP result.
X-Output-Width / X-Output-Height	1600 / 1067	Dimensions after resizing.
X-Quota-Remaining	1874	Conversions left in this month's allowance.
X-Extra-Remaining	0	Extra conversions credited to the account on top of the monthly allowance (usually 0).
X-RateLimit-Remaining	58	Requests left in the current minute for this key.

JSON mode

Send a URL, get a download link

Add ?response=json (or Accept: application/json) and the API answers with JSON: a download link, the sizes and what is left of your allowance. The right mode for images already online, images over the upload limit, automations and AI assistants.

convert-url.sh — bash
curl -X POST "https://www.fastwebpconverter.com/api/v1/convert?response=json" \
  -H "Authorization: Bearer $FASTWEBP_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"url": "https://example.com/images/hero.png", "quality": 80, "max_width": 1600}'

200 OK — json
{
  "filename": "hero.webp",
  "download_url": "https://www.fastwebpconverter.com/dl/Qm8x2kV4nT0pLr7a",
  "expires_at": "2026-10-10T09:14:03.000Z",
  "original_bytes": 2493112,
  "webp_bytes": 287401,
  "saved_percent": 88,
  "width": 1600,
  "height": 1067,
  "animated": false,
  "quota_remaining": 9874,
  "extra_remaining": 0
}

Field	Type	Meaning
filename	string	Output file name.
download_url	string	Link to the WebP file. It expires; download or copy the file to your storage.
expires_at	ISO 8601 date	When the link stops working: 24 h on Free, 72 h on Pro.
original_bytes / webp_bytes	integer	Sizes before and after.
saved_percent	integer	Percentage saved.
width / height	integer	Output dimensions.
animated	boolean	True when an animated GIF or WebP stayed animated.
quota_remaining / extra_remaining	integer	Monthly and extra conversions left.

GET /usage

Check your allowance

GET https://www.fastwebpconverter.com/api/v1/usage with the same header. It costs nothing and is handy for dashboards and pre-flight checks in batch jobs.

200 OK — json
{
  "plan": "pro",
  "monthly_limit": 10000,
  "used_this_month": 126,
  "remaining_this_month": 9874,
  "extra_conversions": 0,
  "resets_at": "2026-11-01T00:00:00.000Z",
  "requests_per_minute": 120,
  "max_url_mb": 25
}

Field	Meaning
plan	free or pro.
monthly_limit / used_this_month / remaining_this_month	This month's allowance and where you stand.
extra_conversions	Extra conversions credited on top of the monthly allowance (usually 0).
resets_at	When the monthly allowance resets (the 1st, UTC).
requests_per_minute / max_url_mb	Your plan's rate limit and URL size limit.

Errors

Errors you can branch on

Every error is JSON, {"error": {"code", "message"}}, with a stable code. Messages are written for people, so you can show them as they are.

Status	Code	When
400	invalid_parameter	A parameter is out of range, the JSON is not valid, or there is nothing to convert.
400	invalid_url	url is not a valid http or https address.
400	blocked_address	url points to a private, local or reserved network address.
401	unauthorized	The key is missing, revoked or wrong.
402	quota_exceeded	This month's allowance is used up. The message says how to continue.
413	file_too_large	The upload is over 4 MB, or the image behind url is over your plan's limit.
415	unsupported_format	The file is not a format the server reads (HEIC and BMP among them).
415	not_an_image	The url answered with something other than an image.
422	fetch_failed	The url could not be downloaded (timeout, 404, empty answer).
422	decode_failed	The image is damaged or could not be decoded.
429	rate_limited	Too many requests this minute for your plan. Retry after the Retry-After header (60 s).
500	internal_error	Something failed on our side. Retry; the conversion is not counted.

400 Bad Request — json
{
  "error": {
    "code": "invalid_parameter",
    "message": "quality must be an integer from 1 to 100."
  }
}

Limits and plans

Free to try, Pro for full access

The allowance is per account, shared by the API, Claude, ChatGPT and MCP clients, and resets on the 1st of each month (UTC). Pro is one plan with everything, paid the way you prefer: $4.99/month, $29/year or $59 once.

Server-side limits per plan

Plan	Price	Server conversions	Images per batch call	Image by URL up to	API requests a minute	Download links kept
Free	Free	50 a month	5	10 MB	10	24 hours
Pro	$4.99/month, $29/year or $59 once	10,000 a month	50	25 MB	120	3 days

Choosing a quality

Photos: quality 75 to 85. 80 is the default and is visually identical to the original for most images.
Screenshots, UI and images with text: 90 or more, so letters and thin lines stay sharp.
Logos, icons and flat graphics: lossless, often smaller than the PNG and pixel-identical.
Oversized photos: set max_width (1600 for full-width images, 800 to 1200 for content images). Resizing saves more than any quality setting; images are never upscaled.

Every account starts on Free with 50 conversions a month, enough to wire up and test an integration. Pro includes 10,000 server conversions a month (fair use), far above what a site's uploads, a catalogue or a CI pipeline usually need. For more, the API plan ($0.50 per 1,000 conversions, no cap) opens soon: join its waitlist below.

Pro

Full access

$4.99/ month

$29 / year ($2.42/month) · $59 once

Full access: every file, every device, your AI assistant and the API. The API and the AI assistants include 10,000 server conversions a month (fair use).

Download every file of every batch, as one ZIP
No daily limit, up to 100 images per batch
Pro on all your devices: sign in anywhere
Convert in Claude, ChatGPT and any MCP client
REST API with your own keys
Images by URL up to 25 MB, animated GIF to animated WebP
Priority support

Get Pro monthly

Yearly, save 52%Lifetime, $59 once

Start free: get a key

Cancel anytime from your account. 14-day money-back guarantee. Prices include tax where it applies.

API

Opening soon

$0.50/ 1,000 conversions

Billed monthly on what you convert. No minimum.

Pay for what you convert, at any volume: apps, CMSs and build pipelines.

Pay per conversion, billed monthly, no cap
Everything in Pro
600 requests a minute, batches of 100
Usage per key and invoices
Volume pricing above 1,000,000 conversions a month

Work e-mail

Monthly volumeOptional

Until it opens, Pro includes the API with a fair-use allowance.

No-code

Zapier, Make and n8n

Use JSON mode: the automation sends the image URL, receives a download link, and the next step stores or uploads the WebP.

Zapier

Webhooks by Zapier, Custom Request: POST, the convert URL with ?response=json, the Authorization header, and a JSON body with url and quality. Map download_url into the next step.

Make

HTTP, Make a request: method POST, body type Raw, content type JSON, the same body. Parse the response and pass download_url to your storage or CMS module.

n8n

HTTP Request node: POST, Header Auth with Authorization: Bearer, JSON body. Use the response's download_url, or ask for the binary and set the response format to File.

Prefer to ask an assistant?

The same conversions work from Claude, ChatGPT, Cursor or Claude Code through the MCP server at https://www.fastwebpconverter.com/api/mcp, signed in with the same account.

AI assistants MCP server

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

Create a free account (an e-mail code or Google), open your account page and press Create key. The key is shown once: store it in an environment variable such as FASTWEBP_API_KEY. You can create several keys, one per server or project, and revoke any of them.

Yes. Every account, free included, gets an API key and 50 conversions a month at 10 requests a minute, enough to wire up and test an integration. Pro is full access ($4.99/month, $29/year or $59 once): 10,000 server conversions a month (fair use) at 120 requests a minute.

The API answers 402 quota_exceeded with a message saying how to continue. The allowance resets on the 1st of each month (UTC). On Free, Pro lifts it to 10,000 server conversions a month (fair use); above that, write to us through the contact page. GET /usage tells you where you stand.

Originals are processed in memory and never stored. In binary mode the WebP is streamed back and nothing is kept. In JSON mode the WebP is stored behind an unguessable download link for 24 hours on Free and 3 days on Pro, then deleted.

JPG, PNG, GIF, WebP, AVIF, TIFF and SVG. Animated GIFs come out as animated WebP. HEIC photos and BMP files are not read on the server: the browser converter handles them (HEIC in Safari). Output is always WebP, lossy or lossless.

Uploads in the request body are limited to 4 MB. Larger images go by URL: up to 10 MB on Free and 25 MB on Pro. Images up to 100 megapixels are accepted.

Yes, with JSON mode: send a JSON body with the image url and ?response=json, and the answer carries a download_url, the sizes and the percentage saved, which the next step of the automation can use.

Monthly and yearly Pro: Cancel anytime from your account. 14-day money-back guarantee. Lifetime is paid once and never renews. After a cancellation your key keeps working on the free allowance.

Ready to automate your image pipeline?

Create a free account, copy your key and convert 50 conversions a month. Go Pro for full access when you need it.

Get a free API key Pro plan