OutSmart DAXon — a native C# port of Saxon-HE 12.9

OutSmart DAXon is a pure-managed XSLT 3.0 / XPath 3.1 / XQuery 3.1 engine for the classic .NET Framework 4.7.2+ and .NET 10 — a complete C# port of Saxon-HE 12.9 (© Saxonica, MPL 2.0). No Java, no IKVM at runtime: one self-contained assembly with no third-party dependencies, for hosts that are stuck on the old Framework where current XSLT 3.0 engines are not an option.

OutSmart DAXon is an independent derivative work. It is not affiliated with, endorsed by, or supported by Saxonica Limited. "Saxon" and "Saxonica" are trademarks of Saxonica Limited and are used here only descriptively, to identify the upstream project this port derives from.

Base version: the port derives from the Saxon-HE 12.9 Java source release, published by Saxonica at https://github.com/Saxonica/Saxon-HE (see also https://www.saxonica.com/).

Build

Prebuilt assembly: latest release.

Or build it yourself:

dotnet build OutSmart.DAXon.sln -c Release

builds OutSmart.DAXon.dll — the whole engine, one self-contained assembly (src/OutSmart.DAXon/).

Note: .gitattributes pins * -text (no CRLF conversion) — the tree contains byte-sensitive embedded data files. If your clone predates that file, run git config core.autocrlf false; git checkout -- . once.

Usage

using System.IO;
using OutSmart.DAXon.Api;

// One Processor per process — reusable and thread-safe. Optional resource limits:
// new Processor(transformTimeout: TimeSpan.FromMinutes(1), maxInputBytes: 150L * 1024 * 1024)
var proc = new Processor();

// Compile once, reuse for any number of transformations (thread-safe).
XsltExecutable exe = proc.NewXsltCompiler()
    .Compile(new StringReader(xsltText), "urn:stylesheet");

// Parse the input document (or Build(filePath) for a file).
XdmNode input = proc.NewDocumentBuilder()
    .Build(new StringReader(inputXml), "urn:input");

// One transformer per transformation — cheap to create, never share between calls.
Xslt30Transformer tr = exe.Load30();
var output = new StringWriter();
tr.SetGlobalContextItem(input, true);
tr.ApplyTemplates(input, proc.NewSerializer(output));
string result = output.ToString();

Expected failures (bad stylesheet, bad input, resource limit hit) arrive as DAXonApiException with standard XSLT/XPath error codes — one try/catch around the transform call is the whole error-handling contract.

Status

The port is verified against the full W3C QT3 (XPath/XQuery 3.1) + XSLT 3.0 test corpora and matches Java Saxon-HE verdict-for-verdict, except 17 cases requiring XML 1.1 input documents, which the .NET XmlReader cannot parse. Hostile inputs cannot kill the process: transformation and compile-time deadlines, input-size caps and adaptive stack guards turn deep recursion / deep JSON / deep regex nesting into catchable coded errors.

The conformance runner lives in tests/QT3Test; it downloads the W3C corpora at pinned revisions, so the result above can be reproduced locally.

How this port was produced

The translation from the Saxon-HE 12.9 Java sources, and the subsequent refactoring, hardening and performance work, were carried out with AI assistance — Anthropic's Claude (Opus 4.8 and Fable 5) — under human direction and review.

Nothing was taken on the model's word. Every change to the engine had to pass:

• the W3C QT3 (XPath/XQuery 3.1) and XSLT 3.0 conformance corpora — 38 554 cases passing against a fixed, documented set of 17 known failures (XML 1.1 input documents, which the .NET XmlReader cannot parse);
• byte-identity gates — selected transform outputs compared byte-for-byte against Java Saxon-HE running the same inputs;
• a spec-derived suite of 489 cases, a multi-threaded equality battery on one shared Processor, and a set of robustness probes (deadlines, caches, stack guards).

License & attribution

Licensed under the Mozilla Public License, Version 2.0 — see LICENSE.

This is a derivative work of Saxon-HE 12.9, © Saxonica Limited, which is itself distributed under the MPL 2.0 (source: https://github.com/Saxonica/Saxon-HE). Per-file Saxonica copyright notices are retained as required by the license. Files modified in the course of this port carry the same MPL 2.0 terms; the modified source is published here in full. The engine has no third-party dependencies.

OutSmart DAXon is maintained by Outbridge (https://outbridge.app/) and is independent of Saxonica.