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A monorepo is a single source-code repository that contains multiple projects. It does not automatically mean those projects make up one application, share one release, or have to ship together. The key choice is whether projects live together in one repository or are maintained in separate repositories.

What is a monorepo?

“Monorepo” is short for “monolithic repository”; it is also sometimes called a multi-package repository. The term describes how code is organized, not how a product is designed or deployed. One repository can contain related projects, unrelated projects, or a mixture of both. Projects may still have separate owners, build processes, and release schedules.

A 2018 review of software-industry and academic literature describes monorepos as single repositories containing multiple projects. It also notes that projects in one repository often share management tools or dependency versions, though neither is a requirement. The review, by Gleison Brito, Ricardo Terra, and Marco Tulio Valente, synthesized 21 grey-literature sources and two academic papers; it found no consensus that one repository strategy suits every team.

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What changes when projects share a repository?

With a monorepo, contributors can work across projects at the same repository revision. That can make it easier to reuse shared code, update a dependency alongside its consumers, or make a change that spans several modules without coordinating separate repository updates. It can also give teams a shared place for development workflows and project discussion.

Those advantages depend on how the repository is managed. Centralizing code does not itself provide clear ownership, healthy code, simple navigation, or a fast build. A large repository can make it harder to find relevant code and can add work around version control, dependency management, testing, and tooling.

Monorepo versus multiple repositories

The practical comparison is about coordination and boundaries, not a universal winner. A monorepo favors making cross-project work within one repository; separate repositories can fit projects that need more independent dependency and release boundaries. A team should weigh the day-to-day cost of coordinating changes against the cost of maintaining a shared codebase and its supporting systems.

Question What a monorepo can offer What to weigh
How often do changes span projects? One change can update multiple projects at a shared revision. If cross-project changes are rare, the coordination benefit may be limited; if common, separate repositories can make those changes harder to coordinate.
How should dependencies and releases work? Projects can use shared source and be updated together when needed. Independently versioned dependencies or release schedules may call for carefully maintained boundaries, whether projects are together or separate.
Can the team keep builds and tests focused? Build tooling can identify targets affected by a change. Without dependency-aware tooling, a shared repository may make broad builds and tests costly.
Can the organization maintain the repository? Shared tools and workflows can be used across projects. Navigation, code health, ownership, and tooling require ongoing attention.
Is migration worth it? Moving related projects together may reduce repeated coordination work. Moving repositories and their workflows also takes effort; the case is stronger when current coordination pain is real and recurring.

Why a monorepo does not automatically make builds faster

Repository layout and build behavior are separate concerns. A monorepo does not, on its own, make builds incremental or tests selective. Large repositories generally need explicit dependency relationships and tooling that can determine which targets a change affects.

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Bazel’s documentation describes one approach: teams define build targets and their dependencies, allowing the build system to predict which programs and tests may be affected by a change. Bazel’s FAQ presents this in the context of Google’s large version-control system; Bazel is an example, not a requirement for adopting a monorepo.

Choose useful target boundaries

Target granularity involves a trade-off. One broad target is easier to describe, but may force the build system to rebuild an entire project. More fine-grained targets can improve caching and scheduling, but require teams to maintain more dependency declarations. Bazel’s dependency guidance explains this balance.

Match the tooling to the workload

Bazel says it is aimed especially at large codebases, mixed compiled languages, multiple deployment platforms, and extensive test suites. Its FAQ also cautions that it may add little value when a project consists of only a few long, sequential steps. The broader lesson is to choose build and test tools based on the work they need to handle, rather than expecting repository centralization to create speed.

What large-scale examples show—and what they do not

Google is a prominent example of operating at monorepo scale, but its setup is not a template every team should copy. Google Cloud reports that its monorepo holds millions of source files and billions of lines of code, has a history of hundreds of millions of changelists, and receives tens of thousands of new changelists each workday. The cited Google Cloud page does not state when those figures were published, so they should not be read as a current measurement.

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Even Google Cloud says some services supplement the monorepo with a separate Git repository to manage open-source software. A monorepo can coexist with other repositories rather than replacing them all.

At a smaller project scale, Babel’s documentation says its officially maintained modules are kept in one repository. Babel lists a shared lint, build, test, and release process; easier coordination across modules; a single place to report issues; easier setup; and cross-module testing among its benefits. It also notes that the codebase can feel larger and more intimidating. These are Babel’s own project observations, not the result of a controlled comparison. See Babel’s monorepo documentation.

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How to decide whether a monorepo fits

  • Look at coordination pain. Count how often a change needs updates across projects, and how much time separate repositories add to that work.
  • Make release and dependency boundaries explicit. Decide whether projects need a shared revision or independent versioning, and how each should consume internal code.
  • Check build and test capacity. Determine whether your tooling can identify affected projects and avoid running unnecessary work on every change.
  • Plan for ownership and code health. Shared code needs clear responsibility and maintainable boundaries; one repository does not create those practices automatically.
  • Include migration cost. Moving repositories also means adapting workflows and tooling. A migration is most compelling when it addresses recurring, concrete coordination costs.

The 2018 literature review describes benefits such as coordinated changes and easier refactoring, alongside challenges including codebase complexity, code health, tooling investment, build and test concerns, and migration. Those trade-offs remain the useful decision framework: choose the structure that best supports your team’s dependencies, releases, workload, and capacity to maintain it.

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