Scaling ArchUnit with Nebula ArchRules

Netflix's JVM Ecosystem team built Nebula ArchRules, a Gradle plugin suite that extends ArchUnit to share and enforce architectural code rules across tens of thousands of Java repositories. The post explains why ArchUnit was chosen over AST-based tools like PMD (bytecode analysis, cross-JVM-language support, type-safe fluent API), then details how rules are authored as standalone or bundled libraries, published as separate Gradle variants, and automatically discovered and run per source set. A concrete case study shows how library authors can detect downstream usage of deprecated, experimental, or internal APIs across 5,000+ repos. Netflix is now running 358 rules detecting nearly 1 million issues, with plans to integrate auto-remediation via OpenRewrite and LLMs.