monorepo

Monorepo, short for monolithic repository, is a software development approach in which code for many projects, libraries, and services is stored in a single version-controlled repository. In contrast, a polyrepo or multi-repo approach keeps each project in its own repository. A monorepo typically contains multiple languages and tooling, with shared dependencies and a centralized build, test, and release process. Teams may rely on robust tooling to isolate changes and prevent unintended effects across the codebase.

Advantages include atomic changes across the entire codebase, easier large-scale refactors, standardized tooling and dependency versions, and improved visibility and cross-team collaboration. A single repository can simplify code reuse and ensure compatibility of libraries and APIs.

Challenges include scaling in very large repos, longer clone and fetch times, increased CI complexity, potential access control and release management issues, and the need for advanced build systems, caching, and tooling to keep builds fast.

Common approaches and tools include Bazel, Pants, Buck, Lerna, and Nx. These tools support incremental builds, selective testing, and hermetic dependencies across languages. Notable examples: Google maintains a very large monorepo with internal tooling; Facebook has used a monorepo strategy with its own tools and Buck; many other large companies use monorepos to coordinate cross-project changes.