Building Modular Monorepos with Melos

Introduction

Managing multiple Flutter packages and applications in a single repository can quickly become complex. A modular monorepo approach helps you share code, enforce consistent tooling, and simplify CI/CD pipelines. Melos is a community tool designed to orchestrate and automate workflows in mono repositories, making it an ideal choice for any Flutter team that wants to scale. In this tutorial, you’ll learn how to build and manage a Flutter melos monorepo with clear package boundaries, shared dependencies, and repeatable tasks.

Setting up Melos in Your Repository

First, install Melos globally:

dart pub global activate melos

Or add it as a dev dependency in a new tool/melos.dart directory. At the root of your repo, create a melos.yaml file:

name: my_flutter_monorepo
packages:
  - packages/*
  - apps/*
scripts:
  bootstrap:
    run: melos exec -- flutter pub get
  format:
    run

This configuration tells Melos to treat every folder under packages/ and apps/ as an individual Dart or Flutter package. You also define custom scripts, like melos bootstrap, that invoke a pub get in every package.

Organizing Packages and Modules

A recommended layout:

• core: Business logic, models, utilities.

• ui_components: Reusable widgets and themes.

• network: API clients and data sources.

• app_mobile & app_web: Platform-specific apps importing shared packages.

Inside each package’s pubspec.yaml, reference other modules by relative path:

dependencies:
  flutter:
    sdk: flutter
  core:
    path: ../packages/core
  ui_components:
    path

This ensures strong modular boundaries, and Melos will handle linking.

Managing Dependencies and Versioning

Monorepos often share versions across all packages. You can use Melos versioning strategies to bump versions consistently:

scripts:
  version:
    run: melos version --no-publish --yes

Running melos version prompts you to select semver bumps and updates each pubspec.yaml. After that, run melos bootstrap to sync dependencies. When you’re ready to publish to pub.dev, use:

melos publish

Melos publishes each package in the correct order, respecting inter-package dependencies.

Running Build Scripts and Tasks

Melos lets you run any CLI command across all or selected packages. For example, run tests everywhere:

melos exec -- sh -c "flutter test"

Or build a common package:

cd packages/network
flutter pub run build_runner build --delete-conflicting-outputs

You can also define these as scripts in melos.yaml for convenience:

scripts:
  test:
    run: melos exec -- flutter test
  gen:
    run

Invoke them with melos run test or melos run gen.

Continuous Integration with Melos

Integrate Melos into your CI pipeline to standardize checks:

• melos bootstrap to install dependencies.

• melos run format -- --set-exit-if-changed to enforce formatting.

• melos run analyze to catch static errors.

• melos run test for unit tests.

Sample GitHub Actions step:

- name: Install dependencies
  run: dart pub global activate melos
- name: Bootstrap
  run: melos bootstrap
- name: Format check
  run: melos run format -- --set-exit-if-changed
- name: Analyze
  run: melos run analyze
- name: Test
  run: melos run test

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Conclusion

Using a Flutter melos monorepo empowers you to maintain modular, scalable codebases, unify tooling, and streamline publishing. Whether you’re managing a handful of packages or dozens, Melos helps automate repetitive tasks and enforce consistency. Embrace this structure for cleaner code sharing and faster iteration cycles.