Why does pdfrender reject external image and font URLs?

Because it never fetches external resources by design. A renderer that follows arbitrary URLs from user-supplied HTML is a server-side request forgery surface; refusing to fetch removes it entirely. The 400 response lists the offending URLs.

How do I embed a custom font in a generated PDF?

Base64-encode the font file and reference it from an @font-face src as a data: URI. The same applies to images and external stylesheets.

Does inlining assets count against the size limit?

Yes. Base64 encoding adds roughly a third to a file's size, and the 2 MiB REST limit applies to the whole payload — so subset fonts and compress images before encoding.

Images and custom fonts in API-rendered PDFs

pdfrender never fetches external URLs — embed images, fonts and CSS as data: URIs instead. Why that design is safer, and how to inline assets.

Last updated 2026-07-26

External http(s) resources	never fetched — a document referencing one is rejected with 400 listing the URLs
Supported instead	data: URIs for images, fonts and stylesheets

pdfrender deliberately never fetches external resources: a public HTML renderer that follows arbitrary URLs is a server-side request forgery (SSRF) vector and makes renders non-deterministic (a slow or changed remote image changes your PDF). Instead, everything ships inside the document as data: URIs:

<img src="data:image/png;base64,iVBORw0KGgoAAA…" alt="logo">

<style>
  @font-face {
    font-family: "Inter";
    src: url("data:font/woff2;base64,d09GMgABAAA…") format("woff2");
  }
  body { font-family: "Inter", sans-serif; }
</style>

Encoding an asset is one line:

base64 -w0 logo.png          # then prefix with data:image/png;base64,

import base64
uri = "data:image/png;base64," + base64.b64encode(open("logo.png", "rb").read()).decode()

Budget

Inlined assets count toward the 2 MiB request cap — base64 adds about 33 % overhead, so keep images sized for print (a 150-300 dpi logo, not a camera original). If a document references an external URL anyway, the API returns 400 external_resource_blocked with the offending URLs listed, so the fix is mechanical.

Try it free

Try it free — 100 renders a month, no card — or check your inlined document in the free browser tool.

FAQ

Why does pdfrender reject external image and font URLs?: Because it never fetches external resources by design. A renderer that follows arbitrary URLs from user-supplied HTML is a server-side request forgery surface; refusing to fetch removes it entirely. The 400 response lists the offending URLs.
How do I embed a custom font in a generated PDF?: Base64-encode the font file and reference it from an @font-face src as a data: URI. The same applies to images and external stylesheets.
Does inlining assets count against the size limit?: Yes. Base64 encoding adds roughly a third to a file's size, and the 2 MiB REST limit applies to the whole payload — so subset fonts and compress images before encoding.