Good answers here already. I'll throw in C4 Model [0] in here. It's a tool to visualize how system components connect at various level. Unit tests, and code w

Good answers here already. I'll throw in C4 Model [0] in here. It's a tool to visualize how system components connect at various level. Unit tests, and code will help you understand the system bottom up. Documenting with C4 will give you an idea how the system is arranged top down. The context, component connections, etc. I'm partial to C4-PlantUML [1] because you can diagram your system using code; you can version it. You don't have to worry about the layout. It gets out of your way. [0]: https://c4model.com/ https://c4model.com/ [1]: https://github.com/plantuml-stdlib/C4-PlantUML https://github.com/plantuml-stdlib/C4-PlantUML