npm-explain

Explain why a specific package is installed

$ npm explain [package_name]

$ npm explain [package_name] --json

$ npm explain [package_name] --include peer

$ npm explain [package_name] --depth 2

npm explain [ ...]

    One or more package specifications (e.g., package-name, package-name@version) to explain their presence in the dependency tree. If omitted, it will attempt to explain the entire tree (though this is typically handled by npm ls).

--json
    Output the dependency explanation as a JSON object. This format is ideal for programmatic parsing and integration into other tools.

--workspace=
    Run the command in the context of a specific named workspace within a monorepo. This limits the explanation to dependencies relevant to that particular workspace.

--workspaces
    Run the command in the context of all configured workspaces in the current project. This is useful for understanding dependencies across an entire monorepo setup.

--include=
    Include specified dependency types (e.g., dev, optional, peer, build) when tracing the dependency path. By default, npm explain usually considers all common dependency types.

--omit=
    Exclude specified dependency types (e.g., dev, optional, peer, build) from the dependency explanation. This helps narrow down the focus to specific types of dependencies.

The npm explain command is a powerful diagnostic tool designed to help developers understand the precise reasons why a particular package is present within their project's node_modules dependency tree. It acts as a dependency tracer, providing a detailed path or paths from the root project or other parent dependencies that ultimately led to the installation of the specified package.

This command is an invaluable resource for debugging complex dependency graphs, resolving version conflicts, or simply gaining clarity on the origin of an unexpected package. It essentially answers the question, "Why is this package here?" by inspecting the resolved dependency tree represented by your node_modules directory and package-lock.json file. It's often used when encountering issues like "phantom dependencies" or when trying to optimize bundle sizes. npm explain is also aliased as npm why-depends, reinforcing its core purpose of explaining dependency relationships within your project.

The output for deeply nested or highly interconnected dependencies can be very verbose and complex to parse manually. It relies on an existing node_modules directory and/or a package-lock.json file to derive its information; without these, its utility is limited. A package might be depended upon by multiple paths, leading to a comprehensive but potentially overwhelming explanation.

The typical output of npm explain begins by identifying the package and its installed version. It then lists one or more paths that lead to this package's installation, often showing the immediate parent dependency and the type of dependency (e.g., dependencies, devDependencies, peerDependencies). For example, it might show:

some-package@1.0.0
node_modules/some-package
another-package@2.0.0 (depends on some-package)
root-project@1.0.0 (devDependency of some-package)

This allows developers to trace the exact lineage of any package in their project.

When faced with unexpected package versions, duplicate installations, or issues stemming from dependency conflicts, npm explain is a first-line debugging tool. By running npm explain , you can identify which parent packages are demanding different versions of a dependency, helping you to understand the conflict and formulate a resolution strategy (e.g., updating a parent dependency, using overrides). It's also crucial for identifying 'phantom dependencies'—packages that are present in node_modules but not explicitly declared in your package.json, often due to transitive dependencies.

The npm explain command was officially introduced with npm v7. Before its introduction, similar functionality was partially available through commands like npm ls with specific options, or via npm why-depends, which npm explain eventually superseded and now serves as an alias for. Its development aimed to provide a more dedicated and user-friendly interface for understanding complex dependency relationships, especially in light of the more robust peer dependency resolution mechanism introduced in npm v7.

npm-ls(1), npm-view(1), npm-prune(1)