Use ChromicPDF to convert a URL to a PDF from Elixir. It drives a local headless Chrome or Chromium process, accepts a URL (or HTML), and can write the result directly to a file:
ChromicPDF.print_to_pdf({:url, "https://example.net"}, output: "example.pdf")For a production application, add ChromicPDF as a runtime dependency, install a compatible Chrome/Chromium executable, and start ChromicPDF under your supervision tree. The sections below show the complete setup, layout controls, failure fixes, and a hosted alternative when you do not want to operate a browser.
What you need before converting a page
- An Elixir application using Mix.
- ChromicPDF (the readme documents a Mix constraint of
~> 1.17; confirm the current release and compatible Elixir/OTP versions before pinning it). - Chrome or Chromium installed in the runtime environment. ChromicPDF controls this browser through headless Chrome.
- Permission for the application process to launch the browser and write the destination PDF.
Ghostscript is optional. ChromicPDF documents it for PDF/A conversion and for concatenating multiple sources; it is not required for a normal single-page URL conversion.
Install ChromicPDF and start its browser process
Add the dependency
In mix.exs, add ChromicPDF to the dependencies that are available at runtime:
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defp deps do
[
{:chromic_pdf, "~> 1.17"}
]
endFetch it with:
mix deps.getThe exact latest version and its browser requirements can change, so check the ChromicPDF v1.17.1 readme and package metadata when creating a new project.
Add ChromicPDF to the supervision tree
The readme instructs applications to start ChromicPDF as a child. In a standard OTP application, add it to children in application.ex:
def start(_type, _args) do
children = [
# Other supervised processes...
ChromicPDF
]
opts = [strategy: :one_for_one, name: MyApp.Supervisor]
Supervisor.start_link(children, opts)
endUse your project’s existing supervisor name and other children; the important part is that the ChromicPDF process is supervised before your code calls it.
Install and verify Chrome or Chromium
Install the browser using the package manager or base image appropriate for your operating system, then verify that the executable can run in the same container or VM as the BEAM application. A deployment image that has Elixir but no browser will fail even though compilation succeeds. The tested configurations listed in the readme include old combinations such as Elixir 1.15.7 with OTP 26.2 and Chromium 119, and Elixir 1.14.0 with OTP 25.1 and Chromium 90. Those rows document historical test environments, not a current compatibility guarantee. Test your exact Elixir, OTP, browser, OS image, and (if used) Ghostscript combination.
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Minimal Elixir call
Once the application is running, pass a URL source tuple and an output path:
ChromicPDF.print_to_pdf(
{:url, "https://example.net"},
output: "example.pdf"
)The call asks the browser to load the external page and writes the generated PDF to example.pdf. Use an absolute destination path when the working directory can vary between development, a release, and a container.
Wrap conversion in your own function
A small module keeps URL validation, destination handling, and error reporting out of controllers or jobs:
defmodule MyApp.WebPdf do
@spec from_url(String.t(), Path.t()) :: :ok | {:error, term()}
def from_url(url, output_path) when is_binary(url) and is_binary(output_path) do
ChromicPDF.print_to_pdf({:url, url}, output: output_path)
end
endCall it from a supervised task, background job, or controller action rather than blocking a web request indefinitely. Check the returned value and confirm that the file exists before you upload or serve it.
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Generate a PDF from HTML instead of a URL
ChromicPDF also accepts HTML strings as sources. This is useful when Elixir renders a template, combines fragments, or needs a self-contained document instead of fetching a public page.
html = """
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
@page { size: A4; margin: 18mm; }
body { font-family: sans-serif; }
</style>
</head>
<body>
<h1>Invoice</h1>
<p>Generated by MyApp</p>
</body>
</html>
"""
ChromicPDF.print_to_pdf({:html, html}, output: "invoice.pdf")Keep external CSS, fonts, images, and scripts reachable from the browser. For reproducible output, prefer absolute asset URLs or embed the assets and ensure the process has network access when the document is rendered.
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Concatenate several sources
The documentation demonstrates concatenating multiple HTML sources. Use that capability when a report consists of separate sections, and install Ghostscript if your chosen workflow requires the documented concatenation or PDF/A features. Confirm the current API shape in the version you install rather than copying an example from an older release unchanged.
Control paper size, margins, and print appearance
Page dimensions
ChromicPDF’s template API includes page-dimension controls; the readme shows size: :a4. Use the template/options API documented for your installed version to select A4 or another supported paper size, then set margins, headers, and footers as needed. Do not assume a screen viewport is the same as the printed page.
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Browser PDF generation follows print media by default. The Puppeteer Page.pdf API documents that Page.pdf() uses the print CSS media type. Print-specific rules therefore affect visibility, colors, and layout:
@media print {
.navigation, .cookie-banner { display: none; }
a { color: #000; text-decoration: none; }
}
If you need the screen stylesheet instead, Puppeteer documents emulating screen media before creating the PDF. Whether and how that low-level control is exposed by your ChromicPDF version must be checked in its current API documentation. To preserve background colors when supported by the browser, use the CSS property -webkit-print-color-adjust: exact, while understanding that printer settings and browser behavior can still affect the result.
Fonts and late-loading assets
PDF fidelity depends on what the target page has loaded: fonts, images, stylesheets, and JavaScript-rendered content. Puppeteer’s PDF guide states that its Page.pdf() waits for fonts by default; that statement describes Puppeteer’s API and is not proof that every Elixir integration waits identically. If a PDF has missing text or blank image boxes, make the page load deterministically, host assets reliably, and use the readiness controls available in your ChromicPDF release.
Handle output for uploads and HTTP responses
ChromicPDF documents two output patterns: write directly to a named path, or provide a callback that receives the generated PDF as a temporary-file path. The callback approach is useful when you need to upload to object storage, stream the file to another service, or delete temporary files after processing. Keep the callback short and move slow uploads to a supervised job so browser workers are not held longer than necessary.
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Common failures and fixes
“Chrome/Chromium executable not found”
Cause: The runtime image lacks a browser, or the executable path is not visible to the application user.
Fix: Install Chrome/Chromium in the same image or VM, verify it can launch under the service account, and follow the executable configuration documented by your ChromicPDF version.
The application crashes during startup
Cause: ChromicPDF was not started under the supervision tree, or its dependency was not fetched in the release.
Fix: Add ChromicPDF to the application’s children, run mix deps.get, and rebuild the release with runtime dependencies included.
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The PDF is blank or missing dynamic content
Cause: The page failed to load, JavaScript has not finished, or required assets are blocked by authentication, network policy, or certificate errors.
Fix: Open the URL from the same deployment environment, inspect browser logs, make authentication and outbound access explicit, and use the library’s documented waiting/readiness options where available. Do not treat a successful file write as proof that the page rendered correctly.
Layout differs from the browser screen
Cause: PDF output uses print media and print pagination, not an unconstrained screen viewport.
Fix: Add @media print rules, set page size and margins, avoid fixed elements that overlap page breaks, and test long tables and images across multiple pages.
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Cause: Relative URLs resolve differently, assets are private, or the browser exits before resources are ready.
Fix: Use reachable absolute URLs or inline assets, provide the required authentication through your application’s page-loading setup, and test from the production container rather than only from a laptop.
Conversion is too slow or unreliable under load
Cause: Each job depends on a real browser, while pages may execute heavy JavaScript or wait on third-party resources.
Fix: Queue conversions, cap concurrency, set job timeouts, cache documents when content is unchanged, and monitor browser-process memory. The cited documentation does not provide a benchmark or a reliability comparison, so measure your own URLs and deployment.
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Running Chromium alongside the BEAM application gives you control, but it also makes browser installation, patching, scaling, and network access your responsibility. A hosted service can be preferable for bursty workloads, multiple deployment environments, or teams that do not want browser dependencies in an Elixir release.
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ScreenshotNeo is a website screenshot API and MCP server. Its URL endpoint returns PNG, JPEG, WebP, or PDF, so an Elixir service can call it over HTTPS instead of supervising Chromium locally. Before capture it accepts the cookie/consent banner like a visitor and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each step can be disabled. Bot checks/CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed, and the response reports the page verdict and billing result in X-Page-Verdict and X-Billed headers.
For a PDF response, make one GET request (adapt the URL and options to your page):
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curl -G "https://api.screenshotneo.com/v1/shot"
-d access_key=YOUR_API_KEY
--data-urlencode url=https://example.net
-o page.pdfSee the ScreenshotNeo documentation for output and capture parameters. It supports full-page capture with lazy images loaded, CSS-selector element capture, dark mode, 12 device presets plus custom viewports, retina scale, PDF paper size/margins/landscape/page ranges, HTML/CSS input, custom JavaScript and CSS, clicks, selector or network-idle waits, ad/tracker/request blocking, headers, cookies, user agents, Authorization, timezone, geolocation, transparent backgrounds, resizing, configurable-TTL caching, signed image links, asynchronous jobs with signed webhooks, bulk capture of up to 100 URLs per call, a usage API, and an OpenAPI specification. Parameter names used by other screenshot APIs also work, which can simplify migration.
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Calling it from Python or Node.js
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://example.net"}, timeout=90)
r.raise_for_status()
open("page.pdf", "wb").write(r.content)const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://example.net' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
if (!res.ok) throw new Error(`HTTP ${res.status}`);
const data = Buffer.from(await res.arrayBuffer());ScreenshotNeo also provides an MCP server with take_screenshot, get_page_info, and capture_pdf tools for Claude, Cursor, and other MCP clients. The Free plan includes 1,000 shots per month with no card; paid plans start at $5 for 3,000 shots, and every feature is available on every plan. Create a free ScreenshotNeo account.
Choosing between ChromicPDF and a hosted API
| Requirement | ChromicPDF in your Elixir app | ScreenshotNeo |
|---|---|---|
| Infrastructure | You install and supervise Chrome/Chromium. | Call an HTTPS endpoint; no local browser process. |
| Input | URL or HTML strings, including composed sources. | URL, with extensive capture and PDF options. |
| Data path | Named file or documented temporary-file callback. | HTTP response, with verdict and billing headers. |
| Special PDF workflows | Optional Ghostscript for documented PDF/A and concatenation. | PDF paper size, margins, landscape, and page ranges through API options. |
| Pricing model | Your browser and compute costs. | Free 1,000 shots/month; paid plans from $5 for 3,000 shots. |
No source cited here establishes that either approach is universally faster or more reliable. Benchmark representative pages, asset sizes, concurrency, and failure recovery in your own environment.
FAQ
Can ChromicPDF convert a private page?
It can load whatever the browser process can access, but the documented material does not specify a universal authentication mechanism. Design authentication and network access explicitly, then test from the deployment environment.
Does converting a URL require Ghostscript?
No. Ghostscript is optional for the documented PDF/A conversion and concatenation workflows; a normal URL-to-PDF call requires Chrome or Chromium.
Can I rely on the old ChromicPDF test matrix for a new release?
No. The listed Elixir, OTP, Chromium, and Ghostscript versions are historical tested configurations. Validate the versions you will actually deploy.
