MB is a simple wrapper around the GN build tool.
It was originally written as part of the GYP->GN migration, in order to provide a uniform interface to either GYP or GN, such that users and bots can call one script and not need to worry about whether a given bot was meant to use GN or GYP.
It eventually grew additional functionality and is now still used even though everything is GN-only.
It supports two main functions:
“gen” - the main gn gen invocation that generates the Ninja files needed for the build.
“analyze” - the step that takes a list of modified files and a list of desired targets and reports which targets will need to be rebuilt.
We also use MB as a forcing function to collect all of the different build configurations that we actually support for Chromium builds into one place, in //tools/mb/mb_config.pyl.
For more information, see: