Bazel vs Pants

Bazel is a free, open-source tool for automating software builds and tests across languages and platforms. Projects define targets in BUILD files using Starlark, which can also be used to create custom rules and macros. Bazel caches prior work and rebuilds what needs to change, while running tasks in parallel. It supports languages including C++, Java, Kotlin, Python, Go, and Rust, with outputs for desktop, server, Android, and iOS. Bazel runs on Linux, macOS, and Windows, and the documentation describes builds with 100,000 or more source files across multiple repositories. Sandboxing can make builds and tests more hermetic, and failures return a non-zero exit code for basic CI integration. Teams can share outputs through a remote cache, but must select and maintain its backend and secure access because it can contain binaries. IDE options include plugins for IntelliJ, Android Studio, CLion, and Visual Studio Code, plus Xcode integration. Bazel is not well suited to uncached deployment steps that change cloud configuration.

Pants is a free build system for codebases of different sizes, focused on Python, Go, Java, Scala, Kotlin, Shell, and Docker. It installs and coordinates development tools such as compilers, code generators, dependency resolvers, test runners, linters, formatters, packagers, and REPLs. By examining import statements, it can infer file dependencies and reduce manual declarations. The engine is written in Rust, and build rules use typed Python 3. Execution includes concurrency, fine-grained invalidation, hermetic runs, caching, and remote execution. Custom rules use the Pants plugin API and share the core rules’ execution semantics. Built-in integrations include Docker, Pex, Protodoc, Thrift, Protobuf, Helm, linting and formatting tools, packaging, and coverage. Lockfiles pin transitive dependency versions and expected SHA256 hashes, which Pants checks against downloaded artifacts. It runs on Linux, macOS, and Windows with WSL 2, subject to stated system requirements. The project is free under the Apache License 2.0 and offers community support through Slack, mailing lists, GitHub, and other channels.