CobaltPDF.WebKit 1.5.0

CobaltPDF.WebKit

WebKit-based HTML → PDF for .NET — the low-memory, Linux-native sibling of CobaltPDF. Same fluent API, same CobaltEngine, one license key for both engines.

• Up to 96% lower idle memory and 57% faster warm renders than the Chromium edition
• Deploys on stock Azure Linux plans — zip-deploy to App Service or Azure Functions, no Docker, no apt install, no custom containers (validated on real Azure infrastructure)
• ~3 MB deployment artifact — the self-contained render engine (~262 MB) downloads once per instance at first start, SHA-256-verified, and is cached from then on

dotnet add package CobaltPDF.WebKit

using CobaltPdf.WebKit;                      // the only line that differs from CobaltPDF

var pdf = await new CobaltEngine()
    .WithPaperFormat("A4")
    .RenderUrlAsPdfAsync("https://example.com");
await pdf.SaveAsAsync("out.pdf");

Migrating an existing CobaltPDF (Chromium) project is a one-line change: swap using CobaltPdf; for using CobaltPdf.WebKit; and recompile — watermarks, encryption, headers/footers, wait strategies, cookies, custom JS, page splitting and the rest of the fluent API work identically.

Benchmark vs the Chromium edition

10 warm renders across example.com, wikipedia.org/Portable_Document_Format, and news.ycombinator.com; steady RSS sampled after each render returned, full subprocess tree included.

On memory-capped hosts (Azure B-series, small containers) that headroom is the difference between "works reliably" and "OOM-killed on image-heavy pages".

Runs everywhere — one NuGet, backend picked automatically

The WSL / Docker / stub switches are development conveniences: on Linux they are ignored and rendering is always native in-process, so dev configuration ships to production unchanged.

Currently published for linux-x64 glibc hosts (Ubuntu 22.04+/24.04, Debian 12+, Fedora 39+ and equivalent container images). Alpine (musl) and arm64 are on the roadmap.

Azure in three commands

// Program.cs
CobaltEngine.SetLicense(Environment.GetEnvironmentVariable("COBALTPDF_LICENSE")!);
CobaltEngine.Configure(o => { o.MinSize = 1; o.MaxSize = 1; });
_ = Task.Run(() => CobaltEngine.PreWarmAsync());   // bundle download off the request path

az functionapp config appsettings set -n <APP> -g <RG> --settings \
    COBALT_BUNDLE_CACHE_DIR=/tmp/cobaltbundle COBALTPDF_LICENSE="<KEY>"
dotnet publish -c Release -o ./publish
func azure functionapp publish <APP>

That's a complete deployment to a stock Linux Functions plan — something a Chromium-based renderer structurally cannot do (its system libraries aren't installable there). Full walkthroughs, including App Service, Docker, ACA and AWS: Deployment guide.

Tuning highlights

CobaltEngine.Configure(o =>
{
    o.MinSize = 1;              // warm workers
    o.MaxSize = 4;              // concurrent renders (~0.5 GB each)
    o.MaxUsesPerBrowser = 5;    // recycle cadence — bounds steady-state memory
    o.MaxMemoryMb = 2048;       // clean error instead of an opaque OOM-kill
});

• Worker recycling (MaxUsesPerBrowser) keeps long-running services at their cold-start memory baseline instead of creeping upward.
• WithoutPostProcessing() returns the engine's raw PDF — ~30 MB less peak memory and faster renders, at the cost of ~70% larger files (skips font subsetting / image re-encoding; watermarks, encryption and metadata are bypassed with it).
• Every render reports its own telemetry: pdf.RenderMilliseconds, pdf.PeakRssMb, pdf.SteadyRssMb — size your plan from real numbers.

Full reference: Configuration.

Air-gapped & self-hosted deployments

No outbound internet at runtime? All supported, in escalating order of control:

1. Ship the bundle in your publish output — place a pre-extracted bundle at AppContext.BaseDirectory/cobalt-webkit-bundle/; it is discovered before any download is attempted.
2. Point at a pre-staged bundle on disk — set COBALT_INLINE_HOME.
3. Self-host the tarball — COBALT_BUNDLE_BASE_URL + COBALT_BUNDLE_SHA256 (Artifactory, S3, internal GitHub; file:/// URLs work too).
4. Pre-bake Docker images — ADD the tarball into your image's cache directory; the library hash-verifies it and skips the download.

Set AutoDownloadBundle = false to hard-fail if any outbound call would occur. Details: The Render Bundle.

Documentation

License

CobaltPDF.WebKit is commercial software — © 2026 Modus Squared Ltd. It is licensed, not sold, under the CobaltPDF Commercial License; see LICENSE.txt in the package for the full terms and THIRD-PARTY-NOTICES.txt for the open-source components it redistributes.

• Evaluation is free — without a license key every feature works and generated PDFs carry a trial watermark.
• One key activates both engines — CobaltPDF (Chromium) and CobaltPDF.WebKit.
• Purchase: cobaltpdf.com/pricing

CobaltEngine.SetLicense(Environment.GetEnvironmentVariable("COBALTPDF_LICENSE")!);

Support

• Documentation: cobaltpdf.com/docs-webkit
• Troubleshooting: cobaltpdf.com/troubleshooting
• Contact: via cobaltpdf.com/contact