NPM — Number of Public Methods

NPM (Number of Public Methods) counts the public methods exposed by classes and interfaces in a file. NPM is the size of the unit’s API surface.

What mehen emits

Key	Type	Description
`npm`	int	Total public methods across classes and interfaces.
`npm.classes`	int	NPM contributed by classes.
`npm.interfaces`	int	NPM contributed by interfaces.
`npm.class_methods`	int	Alias of `npm.classes`.
`npm.interface_methods`	int	Alias of `npm.interfaces`.
`npm.classes_average`	float	Mean public methods per class.
`npm.interfaces_average`	float	Mean public methods per interface.
`npm.total_methods`	int	Alias of `npm`.
`npm.average`	float	Mean public methods per declaration.

Despite the name, this metric has nothing to do with the npm package manager. NPM here stands for Number of Public Methods, a classic CK-style object-oriented metric.

What counts as “public”

Language	Public method is…
Java / Kotlin	A method declared `public` (or with no modifier in Kotlin).
C#	A method, constructor, operator, property, or indexer declared `public`. A member with no access modifier is `private`, and `internal` is assembly-scoped, so neither counts. An interface member is public by default — but since C# 8 it may carry an explicit `private`, `protected`, or `internal` modifier (a default implementation can be a private helper), and an explicit non-public modifier wins.
TypeScript / JS	A class method without `private` / `protected` / `#` prefix.
Python	A method that does not start with `_`.
Ruby	A method not declared `private` or `protected`.

How to read it

Conventional reading:

`npm`	Interpretation
1–10	Small, focused class.
11–25	Normal application class.
26+	God-class candidate.

Pair with WMC to gauge whether the surface is wide and heavy, and with NPA to gauge whether the class encapsulates state.

References

Lorenz, M. & Kidd, J. (1994). Object-Oriented Software Metrics: A Practical Guide. Prentice Hall.
Chidamber & Kemerer (1994). A Metrics Suite for Object Oriented Design. IEEE TSE.

Overview

Size

Complexity

Function & class shape

NPM — Number of Public Methods

What mehen emits

What counts as “public”

How to read it

References

See also

​What mehen emits

​What counts as “public”

​How to read it

​References

​See also

What mehen emits

What counts as “public”

How to read it

References

See also