Which format should I pick?

AVIF for the smallest file, WebP for the best balance of size and support, JPEG when something old has to read it, PNG when you need lossless or transparency.

Is transparency preserved?

Yes, into PNG, WebP and AVIF. Converting a transparent image to JPEG flattens it, because JPEG has no alpha channel at all.

No. Only the encoding changes. Resize first with the resize endpoint if you want both.

Image format converter API

Convert between JPEG, PNG, WebP and AVIF.

Get a free token Full API reference

Endpoint	POST https://astralbatch.com/api/v1/image-convert
Auth	Bearer token, free
Sends	input: base64
Returns	result: base64
option	jpeg \| png \| webp \| avif
Price	Free. 1,000 calls a day, 60 a minute.

When to call it

WebP and AVIF are the single largest saving available on an image-heavy page, often more than half the bytes at the same quality. Converting in the upload path means the modern format exists for everything, not only for the images somebody converted by hand.

For a one-off, the browser version needs no token and never sends your data anywhere: it runs on your own machine.

Example

curl

curl -X POST https://astralbatch.com/api/v1/image-convert \
  -H "Authorization: Bearer ast_YOUR_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"input": "iVBORw0KGgoAAAANSUhEUg...", "option": "avif"}'

response

{
  "tool": "image-convert",
  "result": "AAAAIGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZk1BMUIAAADybWV0...",
  "chars": 18304,
  "ms": 240
}

In your language

JavaScript

const res = await fetch("https://astralbatch.com/api/v1/image-convert", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.ASTRAL_TOKEN}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({"input": "iVBORw0KGgoAAAANSUhEUg...", "option": "avif"}),
});
if (!res.ok) throw new Error((await res.json()).detail);
const { result } = await res.json();

Python

import os, requests

res = requests.post(
    "https://astralbatch.com/api/v1/image-convert",
    headers={"Authorization": f"Bearer {os.environ['ASTRAL_TOKEN']}"},
    json={"input": "iVBORw0KGgoAAAANSUhEUg...", "option": "avif"},
    timeout=30,
)
res.raise_for_status()
result = res.json()["result"]

Parameters

Field	Type	Notes
input	string	Required. The file, base64 encoded. A data: URL is accepted too. Up to 10,000,000 characters per call.
option	string	One of: jpeg, png, webp, avif.

Errors

Errors are RFC 7807 problem documents with a stable type you can branch on.

missing-token	401	No Authorization header.
bad-request	400	input missing or the wrong type.
bad-option	400	option is not one of the listed values.
tool-failed	422	The input could not be processed. detail says why.
quota-exceeded	429	Past 1,000 calls today.

Questions

Which format should I pick?: AVIF for the smallest file, WebP for the best balance of size and support, JPEG when something old has to read it, PNG when you need lossless or transparency.
Is transparency preserved?: Yes, into PNG, WebP and AVIF. Converting a transparent image to JPEG flattens it, because JPEG has no alpha channel at all.
Is the size changed?: No. Only the encoding changes. Resize first with the resize endpoint if you want both.

Other endpoints

A token takes thirty seconds

Free, no card, 1,000 calls a day, and the same token works on astraltext.com, astralpdf.com, astraljson.com and astralbatch.com.

Get a free token