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Take a JPEG screenshot at a custom viewport size in Ruby with Net::HTTP

Two independent knobs, one request: format picks the codec ("jpeg" here — much smaller files for photographic content), and width/height set the viewport the page believes it is being viewed in. 390×844 is an iPhone-class viewport, so responsive pages serve their mobile layout — media queries fire on viewport width, no user-agent tricks needed.

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: "jpeg",
    width: 390,
    height: 844,
})
  http.request(req)
end

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

File.binwrite("mobile.jpg", res.body)

When to pick which format: JPEG compresses gradients and photos far better and has no alpha channel; PNG is lossless and wins on flat UI, text and sharp edges. For mobile-layout QA screenshots at a fixed viewport, JPEG cuts transfer size dramatically with no visible cost. If you need the image to sit on a transparent background, that is PNG territory.

height here is the viewport height — what "above the fold" means for this render. Without full_page you get exactly that viewport; combine full_page: true with a width and the height is measured from the document instead, at which point the viewport height only affects lazy-load behaviour. All three parameters change the cache fingerprint, so a 390-wide render and a 1280-wide render are separate cache entries — as they should be.

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

Header	Meaning
`Content-Type`	image/jpeg for this request.
`X-Cache`	Each distinct width/height/format is its own cache entry.

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

Take a JPEG screenshot at a custom viewport size in Ruby with Net::HTTP

Notes for Net::HTTP

Response headers worth reading

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