Katzebase is a free, open-source document database for Windows and Linux that combines the flexibility of document-based storage with many of the features normally associated with a traditional relational database. Written in C# using .NET 9, it can run as a service or be embedded directly into your application.

A Document Database That Still Feels Like SQL

Katzebase is aimed primarily at developers, particularly C# and .NET developers, who want the flexibility of a document database without completely abandoning the SQL world they already know.

Instead of storing everything in traditional rows with a fixed set of columns, Katzebase stores data as documents containing key-value pairs. Those documents don't all have to follow the same rigid schema, which can be useful when you're building an application where the data may change or different records require different fields.

Where Katzebase gets interesting is that it combines that flexibility with familiar database features. You still get ACID-compliant transactions, indexing, locking, and isolation, along with a SQL-style query language supporting joins, WHERE clauses, grouping, and aggregation.

In other words, you don't have to throw everything you know about SQL out the window just because you're working with documents.

Built With .NET Developers in Mind

Katzebase is written in C# using .NET 9 and gives developers several ways to work with their data. You can use the API, its SQL syntax, or the included management interface, which itself communicates with Katzebase through the APIs.

There's also a NuGet package for adding Katzebase connectivity to your own projects, along with a straightforward API client and Dapper-like querying.

The server normally runs as a service, but the libraries can also be embedded. That makes Katzebase worth a look for internal applications, development tools and specialized software where bringing in a larger database platform might be overkill.

Installing and Getting Started

Installation is straightforward, but there are a couple of things worth knowing.

Katzebase comes from an independent developer and isn't yet well known to Windows reputation systems. Because of that, you may receive an "unknown" warning when running the installer. This isn't a malware detection. It's a reputation warning, something independent software authors unfortunately run into quite often these days.

Katzebase also requires .NET 9. If the required .NET components aren't installed, the installer will prompt you to get them.

When you first launch the management interface, you'll be asked to log in. The documented default username is:

admin

Leave the password blank.

That's convenient for getting started, but you'll obviously want to set an administrator password before making your Katzebase server accessible to other machines.

Moving Data From Microsoft SQL Server

Katzebase includes a separate MSSQL Migration utility for developers who already have data sitting in Microsoft SQL Server.

The utility connects directly to an SQL Server instance using either integrated Windows authentication or a username and password. You can then select the source database and a target Katzebase schema. The migration interface also provides separate options for importing data and indexes.

That's particularly useful if you're an SQL Server developer who wants to experiment with Katzebase using existing data rather than building a test database from scratch.

Keep in mind that this is an MSSQL migration tool, not a general-purpose CSV or JSON importer.

Sample Databases Could Use Better Instructions

The Katzebase website provides several sample databases for download, including AdventureWorks, StackOverflow, WideWorldImporters, and WordList.

The downloads extract into what appears to be Katzebase's native database structure rather than something you feed into the MSSQL Migration utility. Unfortunately, instructions for actually loading these downloaded databases aren't particularly clear.

During our testing, simply extracting the AdventureWorks database and placing it in the Katzebase root did not cause it to appear after restarting the server.

The sample databases are a nice addition, but some documentation explaining exactly how to load them would make getting started considerably easier.

What's Under the Hood?

Katzebase isn't just a simple key-value store. The database engine includes abortable transactions, caching and deferred writes, indexing with partitioning, nested schemas, logging and health monitoring.

Its SQL implementation supports familiar operations including field selection, joins, TOP queries, WHERE conditions, grouping and aggregate functions. More advanced functionality includes scalar functions, system procedures and session variables.

There's also a static analyzer and schema-aware management UI, giving developers tools for actually working with the database rather than simply providing the underlying engine.

Geek Verdict

Katzebase occupies an interesting middle ground. You get the flexibility of storing information as documents while retaining SQL-style queries, transactions, indexes, and many of the database concepts developers already understand.

The combination makes the most sense for C# and .NET developers, particularly those coming from an SQL Server background who want to experiment with document-based storage without learning an entirely different way of working with their data. This probably isn't one for the average home user looking to organize things.

Katzebase is also free and open source, so developers can dig into the source code, use the API directly, or even embed the libraries into their own projects.

The documentation could use a little more work, particularly around the downloadable sample databases, but Katzebase itself is an interesting project with considerably more going on under the hood than you might expect from a relatively unknown database engine.