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Take a retina-quality (2x) screenshot in Node.js with built-in fetch

A default screenshot renders at 1 CSS pixel = 1 image pixel, which looks soft on any modern display and falls apart the moment a designer zooms in. "device_scale": 2 renders the page the way a MacBook does — double density — so text is crisp in decks, docs and social cards.

Below is a complete, runnable Node.js program using built-in fetch, no third-party dependency needed. It reads your API key from the SNAPDOK_KEY environment variable — free keys take about thirty seconds and need no card.

import { writeFile } from "node:fs/promises";

const res = await fetch("https://snapdok.io/v1/render", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.SNAPDOK_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    url: "https://your-app.com/report/42",
    format: "png",
    width: 1280,
    device_scale: 2,
  }),
});

if (!res.ok) throw new Error(`${res.status} ${await res.text()}`);
await writeFile("retina.png", Buffer.from(await res.arrayBuffer()));

The arithmetic to keep in mind: pixel dimensions are width × device_scale, so 1280 wide at scale 2 produces a 2560-px-wide image with roughly 4× the bytes of the 1× version. For thumbnails that will be displayed small, 1× is cheaper and looks identical after downscaling; spend the scale factor where humans will look closely.

If you arrive from Urlbox or ApiFlash muscle memory: device_scale_factor is accepted as an alias and normalised to the same thing — both spellings even share one cache entry, so mixed codebases do not double-render. JPEG ("format": "jpeg") at scale 2 is often the sweet spot for photography-heavy pages: retina sharpness, a fraction of the PNG size.

Same endpoint, one more trick: if the page you are rendering has a form on it, adding "pdf_forms": true to a PDF render brings it back with real, fillable AcroForm fields — a PDF people can type into, not a picture of one. How that works.

Notes for built-in fetch

No dependency needed: fetch is global from Node 18 onward (snapdok's own test suite uses it). The binary-safety detail is res.arrayBuffer() → Buffer.from(...) — reaching for res.text() is the classic way to corrupt a PDF in Node. fetch does not reject on HTTP error statuses, so the res.ok check is load-bearing: without it, an expired key writes a 40-byte JSON error to disk with a .pdf extension.

Response headers worth reading

Header	Meaning
`X-Cache`	Both device_scale spellings hit the same cache entry.
`X-RateLimit-Remaining`	Requests left in the current second.

Full parameter reference: the docs. Hard numbers on caps and timeouts: limits.

Take a retina-quality (2x) screenshot in Node.js with built-in fetch

Notes for built-in fetch

Response headers worth reading

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