A monorepo is a single source-code repository that holds multiple related projects side by side, instead of giving each project its own separate repository. A web app, a mobile app, a shared design library and a set of utilities can all live under one roof, versioned together and easy to change as a unit.
Think of a shared family kitchen versus everyone having their own. In a shared kitchen, there is one set of good knives, one stocked pantry, one fridge, and everybody uses the same well-maintained tools. When the salt runs out, you restock it once and it is there for every meal. A monorepo is that shared kitchen for code: common pieces are kept in one place, and a fix made once is instantly available to every project that uses it. All of this sits on top of version control, usually Git, which tracks the full history of every change.
The main benefit is consistency. A change that touches both the frontend and the backend can be made, reviewed and merged in one pull request, and shared code never goes out of sync. Large monorepos lean on tools like Turborepo or Nx to keep builds quick.
The cost shows up as it grows. Clone the repo and you pull everything, the build pipeline has to figure out which projects a change actually affects, and without guardrails one team’s edit to a shared package can break another team’s app without warning. That is why big monorepos invest early in caching, ownership rules per folder, and CI that tests only the projects a commit really touched.
At TopDevs we use monorepos when a client has several apps that share code, so updates stay consistent everywhere and there is one obvious place to look.
