devDependency

A devDependency is a package that is required only during the development and testing of a software project, not at runtime in production. In the Node.js ecosystem, devDependencies are declared in the package.json file under the devDependencies field. Examples include testing frameworks (such as jest or mocha), build tools (such as webpack or rollup), linters (such as eslint), type-checkers, and other utilities used by developers while building or validating the project.

Management and usage: Package managers install both dependencies and devDependencies by default. In production deployments, devDependencies can be omitted to reduce the footprint of the installed bundle. For npm, this is achieved with commands like npm install --production or npm ci --omit=dev; for other ecosystems and tooling, similar flags or environment settings are used to exclude development-only packages from production installations.

Purpose: The separation between dependencies and devDependencies helps keep production deployments lean, speeds up deployment, and reduces the risk surface by avoiding unnecessary tooling in the running application. It also clarifies which tools are needed to build or test the project versus what is required to run it.

Limitations and considerations: Some libraries may load development tooling at runtime or during a build step, so it’s important to ensure those tools are not required in production. When publishing packages, devDependencies are not installed for consumers by default; they are intended for development workflows, not for running the published product.

See also: dependencies, peerDependencies, optionalDependencies.