Module Graph Assert


1.5.1 (Jun 5, 2021)
Dec 14, 2019
Sep 4, 2021
Josef Raska (jraska)
Josef Raska (jraska)
Andrew Lord (lordcodes)
Davide Ficano (dafi)
Source code

Show card

Module Graph Assert

A Gradle plugin that helps keep your module graph healthy and lean.

Medium Article with complete context.

Why the module dependency structure matters

  • Build speeds can be very dependent on the structure of your module graph.
  • Modules separate logical units and enforce proper dependencies.
  • The module graph can silently degenerate into a list-like structure.
  • Breaking problematic module dependencies can be very difficult, it is cheaper to prevent them.
  • If not enforced, undesirable module dependencies will appear. Murphy's law of dependencies: "Whatever they can access, they will access."

What we can enforce

  • The plugin provides a simple way for defining rules, which will be verified with the task assertModuleGraph as part of the check task.
  • Match module names using regular expressions.
  • Define the order of layers from the top.
    • moduleLayers = [":feature:\\S*", ":lib\\S*", ":core\\S*"]
    • Modules cannot be dependent within a layer and dependencies cannot go against the direction of the layers.
    • Any module with :feature: prefix cannot depend on another with :feature: prefix.
    • :lib prefixed module cannot depend on a :feature: etc.
    • If there are allowed exceptions you can use moduleLayersExclude = [":feature-about -> :feature-legacy-about"]
  • restricted [':feature-[a-z]* -X> :forbidden-to-depend-on'] helps us to define custom rules by using regex -X> regex signature.
  • maxHeight = 4 can verify that the height of the modules tree with a root in the module will not exceed 4. Tree height is a good metric to prevent module tree degeneration into a list.


Apply the plugin to a module, which dependencies graph you want to assert.

plugins {
  id "com.jraska.module.graph.assertion" version "1.5.1"

You can run ./gradlew assertModuleGraph to execute configured checks or ./gradlew check where assertModuleGraph will be included.


Rules are applied on the Gradle module and its api and implementation dependencies by default. Typically you would want to apply this in your final app module, however configuration for any module is possible. Example

moduleGraphAssert {
  maxHeight = 4
  moduleLayers = [":feature:\\S*", ":lib\\S*", ":core\\S*"] // modules prefixed with ":feature:" -> prefix ":lib:" -> prefix :core:
  moduleLayersExclude = [":feature-about -> :feature-legacy-about"]
  restricted = [':feature-[a-z]* -X> :forbidden-to-depend-on'] // regex to match module names
  configurations = ['api', 'implementation'] // Dependency configurations to look. ['api', 'implementation'] is the default

Graphviz Graph Export

  • Visualising the graph could be useful to help find your dependency issues, therefore a helper generateModulesGraphvizText task is included.
  • This generates a graph of dependent modules when the plugin is applied.
  • The longest path of the project is in red.
  • If you utilise Configuration on demand Gradle feature, please use --no-configure-on-demand flag along the generateModulesGraphvizText task.
  • You can set the modules.graph.of.module parameter if you are only interested in a sub-graph of the module graph.
./gradlew generateModulesGraphvizText -Pmodules.graph.of.module=:feature-one
  • Adding the parameter modules.graph.output.gv saves the graphViz file to the specified path
./gradlew generateModulesGraphvizText -Pmodules.graph.output.gv=all_modules

Graph statistics

  • Executing the task generateModulesGraphStatistics prints the information about the graph.
  • Statistics printed: Modules Count, Edges Count, Height and Longest Path
  • Parameter -Pmodules.graph.of.module is supported as well.
./gradlew generateModulesGraphStatistics -Pmodules.graph.of.module=:feature-one