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Guides · Ruby · Net::HTTP

Take a retina-quality (2x) screenshot in Ruby with Net::HTTP

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 Ruby program using Net::HTTP, 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.

require "json"
require "net/http"
require "uri"

uri = URI("https://snapdok.io/v1/render")

res = Net::HTTP.start(uri.host, uri.port, use_ssl: true, read_timeout: 90) do |http|
  req = Net::HTTP::Post.new(uri)
  req["Authorization"] = "Bearer #{ENV.fetch("SNAPDOK_KEY")}"
  req["Content-Type"] = "application/json"
  req.body = JSON.generate({
    url: "https://your-app.com/report/42",
    format: "png",
    width: 1280,
    device_scale: 2,
})
  http.request(req)
end

raise "snapdok error #{res.code}: #{res.body}" unless res.is_a?(Net::HTTPSuccess)

File.binwrite("retina.png", res.body)

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 Net::HTTP

Stdlib only — no gems. The traps Net::HTTP is famous for, all handled in the sample: TLS is not automatic (set use_ssl: true or you will POST in the clear to port 80 and get a redirect); the default read_timeout of 60 s is close enough to real render times that raising it is wise; and the response body is a binary-ready String, but write it with File.binwrite — plain File.write on Windows would mangle line-ending bytes in the PDF. Check is_a?(Net::HTTPSuccess): Net::HTTP never raises on HTTP error statuses.

Response headers worth reading

HeaderMeaning
X-CacheBoth device_scale spellings hit the same cache entry.
X-RateLimit-RemainingRequests left in the current second.

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

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