Monorepo Explained: Benefits, Challenges, and Best Practices

You’re working on a project. The frontend is in one repo, the backend in another, and shared libraries in a third. And you’re switching repos, and hoping versions don’t drift apart.

Now imagine everything in one place. One repo for all your projects, shared code that updates instantly, and changes that flow through in a single commit. 

Monorepos make that happen. That’s why many big tech companies are using it too, such as: 

• Google built Piper with large-scale automation
• Meta scaled Mercurial
• Microsoft runs Windows in a Git monorepo with VFS for Git
• Uber even moved from mono > multi > back to mono once tooling caught up

In this guide, you’ll learn what a monorepo is, how it compares to polyrepos, and the key benefits, challenges, and best practices you should know. 

What Is a Monorepo?

A monorepo (monolithic repository) means one repository. In a monorepo, all your different projects reside in the same place, rather than being split across separate repositories. 

Even though the projects are side by side, they are still independent. This means you can build, test, and deploy them independently, but you also get the benefit of keeping everything together in one spot.

But note that a monolithic application and a monorepo are not the same:  

• A monolithic application (monolith) is a single software application that’s built and run as a single unit, usually working off the same dataset. It can be inside a monorepo (just as one of many projects).
• Monorepo stores and manages code in a way that many projects live in the same repo, but are still independent from one another. 

A monorepo is not a monolithic app. In fact, monorepos often work really well with microservices, because each service can live in the same repo while still being independent.

The concept of the monorepo isn’t new. 

In the early 2000s, major tech companies began adopting a “shared codebase” approach. The idea was simple: instead of scattering code across many repos, put everything in one place to make collaboration easier.

Since then, big tech companies such as Google, Meta, Microsoft, Airbnb, Twitter (X), Uber, and Pinterest have adopted monorepos to manage their large and fast-moving codebases.

Monorepo vs. Polyrepo

The opposite of a monorepo is a polyrepo (multirepo). Let’s see how it’s different.  

Polyrepo

A polyrepo, also called a multirepo, is when each project has its own separate repository. 

For example, the frontend code might be in one repository, the backend in another, and shared libraries on their own. Each repository is managed independently with its own dependencies and workflows.

Monorepo vs. polyrepo. Image by Author.

Quick look at the key differences 

Let's see what the key differences are between monorepos and polyrepos: 

Benefits of a Monorepo

Monorepos come with lots of benefits. Here are a few of them: 

Improved collaboration and visibility

When all the code is in one place, everyone can see what’s going on. You can check out other projects, learn from them, or even lend a hand if needed. 

This makes teamwork smoother, helps different teams work together, and reduces silos.

Simplified dependency management 

If different projects use the same libraries but keep their own versions, things can get messy fast. 

For example, one project uses an older version while another uses a newer one. This can make the code harder to run, and you may spend most of your time fixing the same issue in more than one place.

However, in a monorepo, the shared code resides in a single location. You update it once, and every project gets the fix right away. You don’t have to chase down version mismatches or deal with conflicts between different versions.

Atomic commits and easier refactoring 

Sometimes you need to make a change that affects more than one project. For example, you may want to update a shared library. With a monorepo, you can update that code and apply the fixes to all the projects in one commit. 

This means all the projects stay in sync, so you don’t have to worry about disrupting other code by mistake. 

Consistent tooling and processes

With one repo, there’s one way to build, test, and deploy. You don’t have to remember different setups for different projects. This makes it easy for new team members to start without any confusion. 

Faster iteration for certain workflows

If you have two or more projects that depend on the same code, for example, a shared library or utility, you don’t have to update each project one by one in separate repositories. 

With a monorepo, you update the code once, and all the projects inside that repository get the change immediately. This means, instead of switching between separate repositories, you can make changes in one place and see the impact everywhere at once.

This helps in a few everyday situations: 

• When you refactor shared code, you update the library, and every service that relies on it gets that update immediately. 
• When you’re rolling out a feature that touches more than one app, you can release everything together instead of coordinating across different repos. 
• Even your CI/CD pipelines become simpler because builds and tests run against the same codebase rather than being duplicated.

All of this cuts down on back-and-forth, reduces context switching, and shortens feedback loops. This, as a result, speeds up iteration without extra overhead.

Challenges of a Monorepo

Monorepos bring a lot of benefits, but they also come with some challenges. Here are the main ones:

Scalability and performance issues 

As the repo gets bigger, everyday tasks like cloning, searching, or even opening it in your editor start to slow down. Why? Because Git wasn’t originally built to handle massive codebases. So big companies often feel the strain.

Longer build and test times

Because all the projects exist in the same place, a small change can trigger a lot of extra work for your CI/CD pipeline. Because of this, developers end up sitting around waiting for builds or test suites to finish before they can merge or release their code. 

Over time, these delays can cause additional problems, such as blocking other work and making it more difficult to implement small and frequent changes.

Take Uber, for example: when their Go monorepo hit millions of lines of code, some engineers waited hours for builds and validation to finish before they could merge. 

After some time, they sped things up with tools like Bazel and custom build queues. However, it highlights how quickly CI can become a bottleneck when all your projects share a single repository.

Broken main branch risks 

The main branch is the default branch in Git where the latest stable version of your code exists. In a monorepo, everyone works from this shared branch, so if one change breaks it, the whole team (or company) can be blocked until it’s fixed.

Take Airbnb as an example. They ran a democratic deployment (any engineer could test their work and put it into production without waiting for a release manager). 

It felt fast at first, but as the company grew, managing everything became difficult because all their code was stored in a single, large monorepository. Team members put changes into production simultaneously, and updates conflicted, making it difficult to find the cause of problems.

Access control and security

It’s hard to limit access in a monorepo because all the code, configuration files, build scripts, and other resources are stored together. By default, every developer with repository access can usually view and modify all of these components. 

That’s fine for open collaboration, but it’s a challenge when certain parts, such as security keys, deployment scripts, or proprietary algorithms, require stricter permissions.

For example, a company might keep its website code in the same monorepo. Developers working on the website don’t necessarily need access to production server credentials, but because everything lives in one place, it can be difficult to prevent them from accidentally viewing or editing those sensitive files.

Learning curve for new developers 

For newcomers, a vast repo with lots of projects can feel overwhelming. Why? Because there are so many files and folders that make it hard for them to know where to start or what matters for their work. 

They also need to learn the project’s structure, tools, and dependencies before they can confidently run builds or make changes, which can slow their progress until they become familiar with everything.

Best Practices for Monorepo Management

To make sure a monorepo works seamlessly, here are some things you should do:

• Keep the repo organized in a way that makes sense. Put related projects together, use clear names, and make it easy for anyone to find what they need.
• Avoid long-lived branches. Try trunk-based development, where everyone merges changes into the main branch often. This keeps the repo clean and reduces conflicts. 
• Pin dependencies to specific versions so everyone stays in sync. Upgrade them across the repo at the same time to prevent mismatches. 
• Use modern build tools like Bazel, Buck, Nx, Pants, Rush, or Lerna to make builds faster and handle the complexity of large repos. 
• Don’t rebuild or retest the entire repo if only a small part changed. Use differential builds and targeted testing to save time and give developers faster feedback. 
• Set up Git CODEOWNERS in your VCS platform (e.g., GitHub/GitLab) to protect sensitive areas such as deployment scripts or configuration files, and require the right teams to review changes.

Popular Tools for Monorepo Management

A monorepo may become complicated as projects expand. So, to make things easier, many tools have been built to help with builds, dependencies, and keep everything organized.  

Here are some of the most common ones:

Bazel 

Bazel is an open-source build system created at Google to handle very large and complex codebases. 

Here are some of its key features:

• Fast builds: Rebuilds only what has changed, using advanced caching, optimized dependency analysis, and parallel execution.
• Multi-language support: Works across different platforms and languages, including Java, C++, Go, Android, and iOS, and it works across Windows, macOS, and Linux.
• Scales easily: Handles both massive monorepos and multiple repositories, making it suitable for organizations of any size.
• Extensible: Allows new languages and platforms to be added with its extension system, supported by a growing community.

Bazel is trusted by companies such as Google, Stripe, and Dropbox to build and test mission-critical infrastructure and applications.

Nx

Nx is an open-source toolkit for managing monorepos and is especially popular in JavaScript and TypeScript, with strong support for frameworks like React, Angular, Vue, and NestJS. It helps teams organize multiple apps and libraries in one place, while keeping builds and tests fast. 

Here are some of its key features: 

• Smart task runner: Understands how different parts of your code depend on each other, so it only runs what’s needed and avoids wasting time.
• Works with what you have: Runs existing scripts, like npm or Gradle tasks, so you don’t have to change your setup.
• Nx Cloud: Speeds development lifecycle with remote caching, faster CI runs, and tools that help detect and fix problems automatically.
• Extra tools: Features like Nx Console give you autocomplete, a visual project graph, and easy ways to manage tasks.

Lerna

Lerna is one of the earliest and most trusted tools for managing JavaScript and TypeScript monorepos. It makes it easy to organize multiple packages in a single repository and helps with building, testing, and publishing them.

In fact, some of the most well-known projects, like Create React App, Jest, and NestJS, have used Lerna to manage their packages. 

Some of its key features are: 

• Smart builds: Avoids repeating work by reusing cached results instead of rebuilding the same code again.
• Fast execution: Tasks run in parallel but still respect the order of dependencies.
• Distributed caching: Build results can be shared between developers and CI systems, cutting down build times.
• Package publishing: Simplifies publishing to npm with both shared and independent versioning.
• Scaling: Spread workloads across multiple machines without extra setup.
• Visualization: Comes with tools to show how projects and dependencies connect in your repo.
• Low setup: Requires little configuration, so you can keep your existing npm scripts and run them faster.

Pants

Pants is a fast and user-friendly build system that works well for monorepos of different sizes. It began with a focus on Python but now also supports Go, Java, Scala, Kotlin, Shell, and Docker, with more languages being added. 

That’s why it’s widely used and trusted by companies such as Coinbase, IBM, Slack, Salesforce, and Orca Security, as well as many smaller teams.

Here are some of its key features:

• Easy to adopt: Requires minimal configuration and can infer most build information automatically, which means less boilerplate to maintain.
• Secure builds: Supports multiple dependency resolves and lockfiles, creating reproducible builds that are more resistant to supply chain attacks.
• Flexible: Works at the file level, so it can handle complex or tangled dependency structures without forcing strict modularity.
• Extensible: Offers a plugin system using Python so that teams can customize it for their own needs.
• Git-aware: Detect changes between branches and only run the tests or builds that are affected.

Rush 

Rush is a monorepo tool designed for JavaScript projects that require managing multiple packages within a single repository.

Here are some of its key features: 

• Built for scale: Supports parallel, incremental, and distributed builds so even huge repos stay efficient.

• Team coordination: Keeps dependency versions consistent, reviews new packages before adding them, and supports both shared and independent versioning.
• Reliable installs: Supports pnpm (recommended), npm, and Yarn to make installs predictable.
• All-in-one tool: Handles installs, linking, builds, publishing, version management, and change logs in one place.

Rush is an open-source and trusted platform, used by major products such as Azure SDK, HBO Max, OneDrive, SharePoint, Office 365, and Wix.

Turborepo

Turborepo is a high-performance build system that makes JavaScript and TypeScript monorepos faster and easier to manage. It focuses on solving common scaling issues that arise when multiple apps and packages coexist in the same repository.

Here are some of its key features:

• Remote caching: Saves the results of builds and tests so the same work never has to run twice, cutting down CI times.
• Task scheduling: Runs tasks in the right order and in parallel across all available cores for maximum speed.
• Incremental adoption: Can be added to any repo in minutes, using existing package.json scripts and working with npm, Yarn, or PNPM.
• Lightweight cloning: Allows developers to clone only the parts of a monorepo they need, reducing setup time.
• Optimized workflows: Builds only what has changed, keeping feedback loops fast.
• Familiar developer experience: Works with standard Git workflows and doesn’t require changing how teams already manage code.

Moon

Moon is a fast monorepo management tool written in Rust. It supports languages like JavaScript, TypeScript, Rust, Go, and Ruby.

Here are some of its key features:

• Speed: Uses smart caching and incremental builds so only the changed code is rebuilt.
• Collaboration: Remote caching shares results across teammates and CI.
• Cross-platform: Runs on Linux, macOS, and Windows.
• Project graph: Maps dependencies to help organize and scale large repos.

Lage

Lage is a task runner built for monorepos that focuses on speed and efficiency. It helps teams avoid rebuilding work that’s already been done.

Some of its key features are:

• Skips repeated work: Reuses results locally or from teammates, so builds don’t run twice.
• Fast setup: Easy to configure and works across environments.
• Caching: Supports local cache or external storage to speed up CI pipelines.
• Insights: Includes tools to profile builds and visualize dependency graphs.

Yarn workspaces

Yarn introduced workspaces to make it easier to manage projects that have many packages inside a single repo (a monorepo). 

Here are some of its key features:

• No duplicate installs: Common dependencies are installed only once at the root, so you avoid bloated node_modules in every package.
• Automatic linking: If one package depends on another in the same repo, Yarn will link them for you.
• One lockfile: Has a single yarn.lock for the whole repo, which keeps versions consistent across all packages.

When to Use a Monorepo

Let's look at a few common scenarios when a monorepo would be helpful for you: 

Small to medium-sized teams with shared code

If your team is small and a lot of code is reused across projects, a monorepo can save you time. Because everyone on your team can work in the same place, and shared libraries stay in sync without extra effort. So that’s a win-win.  

Projects with tight dependency relationships

When your different projects depend on each other closely, keep them in one repo. That way, changes can happen together in a single commit instead of juggling multiple repos.

Organizations seeking unified tooling and visibility

With a monorepo, you can set up a unified CI/CD configuration. This doesn’t mean there’s only one pipeline for all projects, but it does mean you can optimize pipelines so they only run the builds and tests affected by recent code changes, which saves time and resources.

But Monorepos aren’t perfect for every case. If your projects are totally independent, or if you need strict access controls (where some teams shouldn’t see specific code), then polyrepos (multiple repos) may be your go-to choice.

Weighing the Pros and Cons

Here’s a quick overview of the advantages and disadvantages of monorepos:

Final Thoughts

A monorepo can make collaboration easier, dependencies simpler, and iteration faster, but it also comes with real challenges around scale, performance, and access. Deciding to adopt one should be a strategic choice based on how your teams are structured, how closely your projects depend on each other, and whether you’re ready to invest in the proper tooling.

But without strong collaboration habits and clear ownership, even the best monorepo setup will struggle. If you’re exploring this path, it’s worth sharpening your fundamentals first. The Software Engineering Principles in Python course is a great place to start. It will help you build the practices that make a monorepo succeed.