XQuery 4.0, XSLT 4.0 and XPath 4.0
for .NET

A complete XML and JSON processing stack, free and open source under Apache-2.0. No Java bridge, no COM interop, no separate server to run. Pure .NET, async throughout.

Get Started Explore the platform

An embedded document database built on the same stack is in development. Register for early access.

Transform a document in a few lines

using PhoenixmlDb.Xslt;

var transformer = new XsltTransformer();
await transformer.LoadStylesheetAsync(stylesheet);
transformer.SetParameter("reportDate", "2026-01-15");

string result = await transformer.TransformAsync(inputXml);

Install with dotnet add package PhoenixmlDb.Xslt

A real document database

In development, not yet published: embedded XML/JSON storage with ACID transactions, MVCC concurrency, and durable typed indexes — backed by LMDB, queried with XQuery.

Standards-based querying, built in

Complete XQuery 4.0, XSLT 4.0, and XPath 4.0 — streaming, higher-order functions, maps, arrays, JSON. They power the database and stand alone as packages. Free and open-source (Apache-2.0).

Pure .NET, free to start

Native NuGet packages, async throughout, no JVM or COM interop. The query engines are open-source today; the database engine is in development and will be free for development use, with paid licenses for production once it ships.

Everything you need for XML/JSON processing

A complete platform for document transformation, querying, and storage.

Transform

XSLT 4.0

XSLT 4.0 with streaming, higher-order functions, maps, arrays, and JSON support.

Query

XQuery 4.0

XQuery 4.0 engine with FLWOR expressions, window clauses, and the update facility.

Navigate

XPath 4.0

XPath 4.0 with arrow operators, lookup expressions, and inline functions.

Automate

CLI Tools

Command-line interface for transforms, queries, and batch processing.

Store

Document Database

Embedded XML/JSON document store with ACID transactions, MVCC, and rich indexing. In development.

Serve

Server Mode

Standalone server with gRPC APIs for processing pipelines and document management. In development.

Built for real work

To the spec

XQuery 4.0, XSLT 4.0, and XPath 4.0 implemented to the W3C specifications — including streaming, maps, arrays, and JSON.

Durable by design

ACID transactions and MVCC over LMDB, designed so indexes and document versions survive restarts. Still in development — the engine is being tested under sustained concurrent load ahead of release.

We run on it

Our own documentation toolchain (Crucible) transforms its sites with the PhoenixmlDb XSLT engine.

Ship PhoenixmlDb inside your product

Building on the PhoenixmlDb database engine? The planned Distribution tier will cover OEM and redistribution rights so you can embed it as a built-in capability — the database engine is still in development and not yet available. The query engines are Apache-2.0 today — redistribute those freely.

Contact for Licensing

Free engines, honest licensing

The engines are Apache-2.0 and always will be. The database engine is in development and will be free for development use when it ships.

Available today

XQuery, XSLT, XPath and the CLI tools.

Free

Apache-2.0. No registration, no limits.

Get Started

Document database

Embedded storage, indexing and transactions.

In development

Free for development when it ships.

See planned licensing

Ready to get started?

The engines are on NuGet now. Install one and run your first transform in minutes.

Read the docs

XQuery 4.0, XSLT 4.0 and XPath 4.0 for .NET