Bundle File Formats

Mercurial supports generating standalone "bundle" files that hold repository data. These "bundles" are typically saved locally and used later or exchanged between different repositories, possibly on different machines. Example commands using bundles are hg bundle and hg unbundle.

Generation of bundle files is controlled by a "bundle specification" ("bundlespec") string. This string tells the bundle generation process how to create the bundle.

A "bundlespec" string is composed of the following elements:

A string denoting the bundle format to use.
Denotes the compression engine to use compressing the raw bundle data.
Arbitrary key-value parameters to further control bundle generation.

A "bundlespec" string has the following formats:

The literal bundle format string is used.
The compression engine and format are delimited by a hyphen (-).

Optional parameters follow the <type>. Parameters are URI escaped key=value pairs. Each pair is delimited by a semicolon (;). The first parameter begins after a ; immediately following the <type> value.

Available Types

The following bundle <type> strings are available:


Produces a legacy "changegroup" version 1 bundle.

This format is compatible with nearly all Mercurial clients because it is the oldest. However, it has some limitations, which is why it is no longer the default for new repositories.

v1 bundles can be used with modern repositories using the "generaldelta" storage format. However, it may take longer to produce the bundle and the resulting bundle may be significantly larger than a v2 bundle.

v1 bundles can only use the gzip, bzip2, and none compression formats.


Produces a version 2 bundle.

Version 2 bundles are an extensible format that can store additional repository data (such as bookmarks and phases information) and they can store data more efficiently, resulting in smaller bundles.

Version 2 bundles can also use modern compression engines, such as zstd, making them faster to compress and often smaller.

Available Compression Engines

The following bundle <compression> engines can be used:


An algorithm that produces smaller bundles than gzip.

All Mercurial clients should support this format.

This engine will likely produce smaller bundles than gzip but will be significantly slower, both during compression and decompression.

If available, the zstd engine can yield similar or better compression at much higher speeds.


zlib compression using the DEFLATE algorithm.

All Mercurial clients should support this format. The compression algorithm strikes a reasonable balance between compression ratio and size.


No compression is performed.

Use this compression engine to explicitly disable compression.


Produce a v2 bundle using default options, including compression.
Produce a v1 bundle with no compression.
Produce a v2 bundle with zstandard compression using default settings.
This errors because zstd is not supported for v1 types.