Bazel - Google's Build System That Might Ruin Your Life

Google released Bazel in 2015 because their internal Blaze was dealing with shit no other build system could touch. 2 billion lines of code, tens of thousands of engineers all committing at once.

Your cute 50,000-line Node.js app? That's a rounding error to them.

The Problems It Actually Solves

Your Builds Are Inconsistent as Fuck: Ever had a build work on your machine but fail in CI?

Or pass in CI but fail on your coworker's laptop? Bazel's hermetic builds sandbox everything so the only inputs are what you explicitly declare.

No more mystery failures because Bob has a different Python version installed.

Rebuilding Everything Takes Forever: Bazel tracks dependencies at a granular level and only rebuilds what actually changed. Spotify went from 80-minute iOS builds to 20 minutes.

That's not theoretical

• that's "I can actually get coffee instead of planning my day around build time."

You Have Multiple Languages and They Hate Each Other: Most build systems are single-language. Maven for Java, go build for Go, npm for JavaScript

• all with different conventions and tooling.

Bazel lets you build Java microservices, C++ libraries, Go backends, and React frontends in one workspace with consistent rules.

The Scale Where It Makes Sense

Bazel isn't for everyone.

If you have under 100 developers or a single-language project, you'll probably spend more time fighting Bazel than benefiting from it. This is for teams with Google-scale problems:

• Uber: 900+ active developers, 70,000+ files in Go monorepo
• Dropbox:

Production releases across Type

Script, Python, Go, C, and Rust

• Twitter (back when it existed):

Monorepo with hundreds of services

The caching system shares build artifacts across your entire team.

When someone builds a target, everyone else gets the cached result instantly. For large teams, this means build times go from hours to minutes.

When You Should Run Away

Don't use Bazel if:

• You have under 100 developers (the migration cost isn't worth it)
• Single language project (Gradle, Maven, or language-native tools work fine)
• Your team doesn't have dedicated build infrastructure expertise
• You can't afford 6-18 months of reduced productivity during migration

**The learning curve isn't steep

• it's a fucking cliff.** Bazel has its own language (Starlark), its own bizarre concepts (packages, targets, rules), and its own twisted way of thinking about dependencies.

Your team will hate you for the first 6 months. I guarantee it.

The Honest Performance Story

Yes, Bazel can be faster. But for typical incremental builds, Gradle actually outperforms Bazel by 5-16x. Bazel wins on clean builds and when you have massive dependency graphs, but if you're just doing normal development, Gradle's daemon and incremental compilation are often faster.

The real win is reliability and scale, not speed.

If you've made it this far and you're still thinking about migrating to Bazel, you need to understand what you're actually signing up for. The features sound impressive, but the migration reality is brutal. Read on to understand what actually goes wrong during Bazel migrations and whether your team can survive the process.

Okay, you're still reading, so maybe you're one of the unlucky souls who actually needs Bazel. Here are the features that might justify putting your team through migration hell.

Caching That Actually Works (Unlike Everything Else)

Most build systems have shitty caching. Bazel's caching is the one thing they got absolutely right:

Content-Based Hashing: Instead of relying on timestamps (which lie), Bazel hashes file contents. Change one character in a massive file? Only that file and its direct dependents rebuild. Your IDE changing modification times randomly? Bazel doesn't give a fuck.

Remote Caching That Shares: When your coworker builds something, you get their results instantly. No more "works on my machine" followed by 20-minute rebuilds. This is the difference between Bazel and everything else - shared team cache that actually works.

Distributed Builds: Got a big project? Bazel can run your build across hundreds of machines. Google runs builds with thousands of concurrent actions. Your laptop becomes just the orchestrator while AWS does the heavy lifting.

Remote execution distributes build actions across a cluster of machines, with your local machine acting as the orchestrator while compute-heavy tasks run on remote workers.

The catch? Setting up remote execution is a nightmare that will consume 2-3 months of your infrastructure team's life.

Starlark: Python's Weird Cousin

Bazel uses Starlark for build configuration. It looks like Python but with restrictions:

def _my_rule_impl(ctx):
    # This looks like Python but you can't do I/O
    # or call random functions
    return [DefaultInfo(files = depset(ctx.files.srcs))]

my_rule = rule(
    implementation = _my_rule_impl,
    attrs = {"srcs": attr.label_list(allow_files = True)},
)

The Good: You can write actual logic instead of XML hell. Rules are composable and reusable across projects.

The Bad: It's Python but castrated. No network calls, no file I/O, no imports. Debugging is harder than normal Python because stack traces are useless.

The Ugly: Your team will spend months learning Bazel-specific concepts that transfer nowhere else.

Query Tools That Are Actually Useful

Bazel's query system is legitimately great for understanding large codebases:

## What depends on this library?
bazel query "rdeps(//..., //lib/database:client)"

## What would break if I change this?
bazel query "allrdeps(//core/auth:service)"

## Visualize the dependency mess
bazel query --output=graph "deps(//app:main)" | dot -Tpng > deps.png

This is gold when you have 50+ services and can't remember which ones call which libraries.

Current State and What's Coming

Bazel 8.4.0 (literally released today, September 4, 2025) includes:

• System trust store support (finally, no more certificate hell)
• Better macOS XDG directory support
• Improved C++ cross-compilation

The Big Change Coming: Bazel 9.0 will kill the WORKSPACE system entirely. If you're still using WORKSPACE files, start migrating to Bzlmod now or get fucked when 9.0 drops. The migration isn't automatic and the tooling is half-baked.

Remote Execution Improvements: They're working on async execution, which should help with parallelism. Current remote execution has some bottlenecks that make it slower than it should be.

The Reality Check

These features are impressive on paper. In practice:

• Caching: Works great once configured, takes 2-3 attempts to get right (first attempt will definitely fail)
• Remote Execution: Powerful but expensive as fuck and complex to set up
• Starlark: Flexible but has a learning curve that will break your spirit
• Query Tools: Actually useful from day one (the only thing that just works)

The question isn't whether Bazel has cool features - it does. The question is whether those features are worth 6+ months of reduced productivity while your team learns a completely new way of thinking about builds.

Before you make that decision, you need to see how Bazel actually compares to the build tools you already know. Not marketing fluff - real performance data and honest trade-offs that matter for day-to-day development.