Named Binary Tag (NBT) is a structured binary file format used by Minecraft. fNbt is a small library, written in C#. It provides functionality to create, load, traverse, modify, and save NBT files and streams. The library provides a choice of convenient high-level APIs (NbtFile/NbtTag) that present an object model, or lower-level higher-performance APIs (NbtReader/NbtWriter) that read/write data directly to/from streams.

Current released version is 1.0.0 (3 July 2025).

fNbt is based in part on Erik Davidson's (aphistic's) original LibNbt library, now completely rewritten by Matvei Stefarov (fragmer).

FEATURES

• Load and save uncompressed, GZip-, and ZLib-compressed files/streams.
• Easily create, traverse, and modify NBT documents.
• Simple indexer-based syntax for accessing compound, list, and nested tags.
• Shortcut properties to access tags' values without unnecessary type casts.
• Compound tags implement ICollection<T> and List tags implement IList<T>, for easy traversal and LINQ integration.
• Good performance and low memory overhead.
• Built-in pretty-printing of individual tags or whole files.
• Every class and method are fully documented, annotated, and unit-tested.
• Can work with both big-endian and little-endian NBT data and systems.
• Optional high-performance reader/writer for working with streams directly.

DOWNLOAD

Latest version of fNbt targets .NET Standard 2.0, which means it can be used in .NET Framework 4.6.1+, .NET Core 2.0+, Mono 5.4+, and more.

• Package @ NuGet: https://www.nuget.org/packages/fNbt/

• Compiled binaries and single-source-file amalgamations: https://github.com/mstefarov/fNbt/releases

EXAMPLES

Loading a gzipped file

    var myFile = new NbtFile();
    myFile.LoadFromFile("somefile.nbt.gz");
    var myCompoundTag = myFile.RootTag;

Accessing tags (long/strongly-typed style)

    int intVal = myCompoundTag.Get<NbtInt>("intTagsName").Value;
    string listItem = myStringList.Get<NbtString>(0).Value;
    byte nestedVal = myCompTag.Get<NbtCompound>("nestedTag")
                              .Get<NbtByte>("someByteTag")
                              .Value;

Accessing tags (shortcut style)

    int intVal = myCompoundTag["intTagsName"].IntValue;
    string listItem = myStringList[0].StringValue;
    byte nestedVal = myCompTag["nestedTag"]["someByteTag"].ByteValue;

Iterating over all tags in a compound/list

    foreach( NbtTag tag in myCompoundTag.Values ){
        Console.WriteLine( tag.Name + " = " + tag.TagType );
    }
    foreach( string tagName in myCompoundTag.Names ){
        Console.WriteLine( tagName );
    }
    for( int i = 0; i < myListTag.Count; i++ ){
        Console.WriteLine( myListTag[i] );
    }
    foreach( NbtInt intItem in myIntList.ToArray<NbtInt>() ){
        Console.WriteLine( intItem.Value );
    }

Constructing a new document

    var serverInfo = new NbtCompound("Server");
    serverInfo.Add( new NbtString("Name", "BestServerEver") );
    serverInfo.Add( new NbtInt("Players", 15) );
    serverInfo.Add( new NbtInt("MaxPlayers", 20) );
    var serverFile = new NbtFile(serverInfo);
    serverFile.SaveToFile( "server.nbt", NbtCompression.None );

Writing to stream directly using NbtWriter

using (var fileStream = File.Create("foo.nbt", bufferSize: 4 * 1024)) {
    var writer = new NbtWriter(fileStream, "Server");
    writer.WriteString("Name", "BestServerEver");
    writer.WriteInt("Players", 15);
    writer.WriteInt("MaxPlayers", 20);
    writer.EndCompound();
    writer.Finish();
}

Constructing using collection initializer notation

    var compound = new NbtCompound("root"){
        new NbtInt("someInt", 123),
        new NbtList("byteList") {
            new NbtByte(1),
            new NbtByte(2),
            new NbtByte(3)
        },
        new NbtCompound("nestedCompound") {
            new NbtDouble("pi", 3.14)
        }
    };

Pretty-printing file structure

    Console.WriteLine( myFile.ToString("\t") ); // tabs
    Console.WriteLine( myRandomTag.ToString("    ") ); // spaces

Check out unit tests in fNbt.Test for more examples.

API REFERENCE

Online reference can be found at http://www.fcraft.net/fnbt/v1.0.0/

LICENSING

fNbt v0.5.0+ is licensed under 3-Clause BSD license; see docs/LICENSE.txt. LibNbt2012 up to and including v0.4.1 kept LibNbt's original license (LGPLv3).

VERSION HISTORY

See docs/Changelog.md