bazel

Bazel is a build system — a tool that takes your source code and turns it into runnable software, handling compilation, linking, testing, and all the steps in between. Its tagline is "Fast, Correct — Choose two," meaning it delivers both speed and reliability where many traditional build tools force a trade-off.

The key to Bazel's speed is that it only rebuilds what has actually changed. If you modify one file in a large codebase, Bazel rebuilds only the parts of the project that depend on that file, skipping everything else. It does this through precise dependency tracking — it knows exactly what each piece of code depends on, so nothing is rebuilt unnecessarily. It also supports distributed caching, meaning build results can be shared across a whole team: if a colleague already built the same code, you download their cached result instead of rebuilding.

Bazel supports multiple programming languages in a single project — including Java, C++, Android, iOS, and Go — making it well-suited for large companies or open-source projects with mixed-language codebases. It is designed to scale from small projects to massive "monorepos" (a single repository containing millions of files and many teams' code). The system is extensible via a scripting language, allowing teams to add support for new languages and platforms.

You would use Bazel if you work on a large codebase where build times have become a bottleneck, or if your project spans multiple languages and needs a consistent, reliable build and test workflow across platforms. The tech stack is Java.