Do you have a module overview document for your Modular Monolith?

A common pain in large modular monoliths (MoMo's) is new devs trying to work out what each module does, leading to confusion, slow onboarding and sometimes even accidentally duplicated code. Without an understanding of the module structure, teams waste time discovering module responsibilities.

"A well-maintained module overview is the map that keeps your monolith navigable as it grows."

Why you need a module overview document

• Faster onboarding: New developers can quickly understand the system's structure and purpose of each module
• Reduced duplication: Teams avoid building the same functionality twice by knowing what's already there
• Reduced Tech Debt Avoid things going in the wrong module and creating tech debt
• Better communication: A shared reference for discussions about architecture and future changes

What does a good module overview look like?

A good overview document (e.g., MODULES.md or docs/modules-overview.md) should:

• List every module, its purpose, and key dependencies
• Be updated whenever modules are added, removed, or changed
• Be easy to find at the root or in the documentation folder
• Use a table to clearly show module names, types, and links to their documentation

Some modular monolith solutions have two types of modules:

• Web API modules (external, exposed to the internet via rest APIs)
• Service modules (internal, available via CQRS Mediatr queries and commands)

Example - Northwind 365 Module Overview