The PhoenixmlDb platform

A full XQuery 4.0, XSLT 4.0, and XPath 4.0 engine for .NET, built from the ground up — with an embedded document database on the same stack still in development.

Query & transform engines

A full XML/JSON processing stack — XQuery 4.0, XSLT 4.0, and XPath 4.0 — that powers the database and stands on its own as open-source NuGet packages. No Java dependency. No COM interop. Pure .NET, async throughout.

✓ XSLT 4.0 with streaming and higher-order functions
✓ XQuery 4.0 with FLWOR, window clauses, update facility
✓ XPath 4.0 with arrow operators and inline functions
✓ Full JSON support via maps and arrays
✓ Extension functions in C#

Document Database In development

An embedded document store optimized for XML and JSON documents with ACID transactions, MVCC concurrency, and rich indexing for fast queries.

✓ LMDB-backed storage (memory-mapped, crash-safe)
✓ ACID transactions with MVCC
✓ Path, value, and full-text indexes
✓ XQuery-native document querying
✓ Container-based organization
✓ Embeddable deployment; server mode is planned

Architecture

  +-------------------------------------------------------+
  |                    Your .NET App                       |
  +-------------------------------------------------------+
            |                           |
  +---------v---------+     +-----------v-----------+
  | XSLT / XQuery /   |     |   Document Database   |
  | XPath 4.0 Engine  |     |    (LMDB Storage)     |
  |  Apache-2.0 (OSS) |     |   In development      |
  +-------------------+     +-----------------------+
            |                           |
  +---------v---------------------------v-----------+
  |              PhoenixmlDb Core                    |
  |    XDM Model  |  Indexing  |  Serialization      |
  +--------------------------------------------------+

Available today

# The query & transform engines — free and open source (Apache-2.0)
dotnet add package PhoenixmlDb.Xslt
dotnet add package PhoenixmlDb.XQuery

# Command-line tools
dotnet tool install --global PhoenixmlDb.Xslt.Cli
dotnet tool install --global PhoenixmlDb.XQuery.Cli

The database engine is still in development and is not yet published. Register for early access →

How licensing will work

The engines are free and always will be. The database engine is free for development — you pay only to run it in production or to ship it inside something you distribute.

Tier	What it covers	Cost
Engines	XQuery 4.0, XSLT 4.0, XPath 4.0 and the CLI tools. Apache-2.0, no registration, no limits.	Free, always
Developer	The full database engine for development, testing, CI, evaluation and internal prototypes. Per seat — one person, as many machines as you work on.	Free, registration required
Production	Running the database engine against real users or real business data.	Planned
Distribution	Embedding the database engine in a product you distribute or resell, including marketplace listings.	Talk to us

Planned licensing. The database engine is not yet available and nothing is purchasable today.