pants

A build system is a tool that automates the process of taking source code and producing runnable software. In large projects, this involves compiling code, running tests, packaging outputs, and sometimes deploying to servers. Rather than running each of these steps by hand, a build system tracks what needs to happen and does it in the right order.

Pants is a build system designed for monorepos. A monorepo is a single code repository that contains multiple projects or services, often written in different programming languages. Many companies use monorepos because they make it easier to share code across projects and keep everything coordinated. The downside is that builds across a large monorepo can become slow, because the build system has to figure out what changed and what needs to be rebuilt.

Pants addresses this by tracking explicit dependencies between parts of the codebase. Instead of rebuilding everything when anything changes, it rebuilds only what is affected by a given change. It also caches results: if a piece of code was already built and its inputs have not changed, Pants reuses the previous output rather than repeating the work. This makes repeated builds faster even in very large codebases.

Other features listed in the project include concurrent execution (running multiple build tasks at the same time), remote execution (offloading builds to remote machines), and a unified interface for working with multiple programming languages. Pants also has a plugin API that lets teams extend the system with custom tools or workflows. Documentation is available at the project website.