NBTExplorer is an open-source NBT editor for all common sources of NBT data. It's mainly intended for editing Minecraft game data.

NBTExplorer supports reading and writing the following formats:

• Standard NBT files (e.g. level.dat)
• Schematic files
• Uncompressed NBT files (e.g. idcounts.dat)
• Minecraft region files (*.mcr)
• Minecraft anvil files (*.mca)
• Cubic Chunks region files (r2*.mcr, r2*.mca)

Windows XP or later, .NET Framework 2.0 or later.

NBTExplorer is compatible with recent Mono runtimes, at least 2.6 or later. Minimally, your system needs the mono-core and mono-winforms packages, or whatever package set is equivalent.

A separate Mac version with a native UI is available. All Mono dependencies are included within the app package. Minimum supported OS is OSX 10.8 Mountain Lion, but it may run on versions as early as Snow Leopard.

The Windows version of NBTExplorer can still be used if the Mac version does not work. You will need to install the Mono runtime, and then run NBTExplorer with Mono from the command line.