When to Use a Monorepo

Source: Dev.to

Do you really need a monorepo?

For many teams, the honest answer is: probably not at first—but it depends heavily on why you think you want one.

Most teams arrive at the monorepo discussion because they’re tired of duplicating code and types across services and frontends. The story is familiar: you start with a backend, add a frontend, then maybe a mobile app, and suddenly you’re copy‑pasting types, request/response shapes, and utilities everywhere. You try to extract an npm package, discover that maintaining and versioning it is painful, and then start looking seriously at monorepo solutions like Turborepo or Nx.

A monorepo is a single repository that contains multiple apps, services, and libraries. Companies like Google and Meta made them famous, and tools like Turborepo and Nx have brought that model to everyday teams.

Typical motivations include:

• Shared code and type definitions across multiple projects
• Simplified dependency management
• Consistent tooling and CI pipelines
• Easier refactoring across the whole codebase

These are real benefits—but they come with notable tradeoffs.

The Hidden Costs of Monorepos

Despite the appeal, monorepos are not free. Tools like Nx and Turborepo are powerful but introduce significant complexity and a learning curve. Nx, in particular, functions as a sophisticated build system and project‑graph manager, offering task‑graph analysis, incremental builds and caching, and a plugin ecosystem.

To really benefit from Nx, teams often need a solid understanding of:

• TypeScript project references
• Path mappings and module resolution
• How build targets (build, test, lint) compose

For less experienced teams—or teams without strong TypeScript and tooling expertise—this can be a real barrier. The tool can feel almost magical until something breaks, at which point debugging becomes difficult. The breadth of Nx’s capabilities, as visible in its documentation, hints at this complexity.

Over time, this can create a tightly coupled system where simple changes fan out widely, increasing both risk and cognitive load. Tooling and CI can become challenging as well: while monorepo tools promise faster builds, misconfiguration may lead to:

• Longer CI times due to unnecessary rebuilds
• Complex caching strategies that are hard to tune
• Hard‑to‑track dependencies causing unexpected breakages

Without carefully tuned CI and development tooling, you can end up worse off than with multiple simpler repositories, undermining the original reasons for adopting a monorepo.

Alternatives to a Monorepo

Before committing to a monorepo, many teams experiment with shared npm packages to avoid duplication. They extract common code into packages like @your-org/api-types or @your-org/utils, host them on a private registry (e.g., GitHub Packages or a self‑hosted npm), and consume these packages from both frontend and backend.

This approach solves some problems but introduces new ones:

• Versioning overhead – every change requires bumping the version, publishing, and updating all consuming applications.
• Drift – backends and frontends can fall out of sync if they don’t upgrade together, leading to subtle incompatibilities.
• Infrastructure cost – maintaining a private registry, authentication, and separate CI pipelines for the shared libraries.

One of the core reasons teams reach for monorepos is the desire to avoid rewriting the same types and clients everywhere. Rather than manually maintaining a shared TypeScript library, another option is to generate types and client code from an API specification.

If your API is well described via OpenAPI or Swagger, you can generate types and client code for each consumer. Tools like Hey API take an OpenAPI spec and output TypeScript types and API client code for web, mobile, and other environments. In this model, the OpenAPI document becomes the contract between backend and frontend, replacing shared TypeScript code with a shared specification.

Benefits of API Specification‑Driven Development

• Single source of truth for API contracts
• Automatic generation of up‑to‑date types and clients
• Reduced need for manual synchronization between services
• Compatibility with multiple languages and platforms via code generators (e.g., OpenAPI Generator, openapi-typescript)

When a Monorepo Makes Sense

There are clear situations where a monorepo is probably worth the added complexity. You should seriously consider a monorepo with Nx, Turborepo, or similar tools if you have multiple actively developed applications that heavily share code—for example:

• An admin panel, a public web app, several backend services, and a shared UI library
• Frequent cross‑project coordination and refactoring
• A need for consistent linting, testing, and build pipelines across the entire codebase

In such environments, code reuse is substantial and the benefits of a unified repository can outweigh the overhead.

Originally published at make-it.run