npm-check-updates (ncu)

npm-check-updates upgrades your package.json dependencies to the latest versions while preserving your existing version-range policy (^17.0.2 → ^18.3.1). It only modifies package.json; the user must run their package manager's install command (e.g. npm install) to update package-lock.json and node_modules.

The CLI is exposed as npm-check-updates and the shorter ncu. The library is pure ESM, importable from Node (and loadable from CommonJS via require()).

When to reach for this skill

• Listing outdated dependencies in a project.
• Bumping versions in package.json to the newest available (dry run, interactive, or write to disk).
• Bulk-upgrading with filters, rejections, peer-dependency awareness, or engine constraints.
• Scanning monorepos (workspaces, --deep, custom globs).
• Safer upgrades via cooldown windows or the iterative --doctor mode.
• Driving ncu programmatically from a Node script or a .ncurc.* config.

Quick start

# Dry run: print upgrades without touching files.
ncu

# Write the upgrades back into package.json, then install.
ncu -u
npm install

# Interactively pick which packages to upgrade.
ncu -i

# Only a subset of packages.
ncu -f "react,react-dom"
ncu "/^@types\//"

# Bump only patch / minor versions.
ncu --target patch
ncu --target minor

# Skip a package.
ncu -x typescript,eslint

Critical flags

Config file (.ncurc.*)

ncu reads config from these locations (later overrides earlier): CLI flags → local .ncurc.* → project .ncurc.* → $HOME/.ncurc.*.

Supported file types: .ncurc, .ncurc.json, .ncurc.yaml, .ncurc.yml, .ncurc.js, .ncurc.mjs, .ncurc.cjs.

From v21 the project is pure ESM, so .ncurc.js should use ESM export default; CJS configs must use .cjs.

A .ncurc.js is also the only place to use predicate functions, e.g.:

export default {
  filter: name => !name.startsWith('internal-'),
  reject: ['@types/*'],
  target: 'minor',
  cooldown: 7,
  doctor: false,
}

Programmatic API

import ncu from 'npm-check-updates'

const upgraded = await ncu({
  packageFile: './packages/app/package.json',
  filter: ['react', 'react-dom'],
  target: 'latest',
  upgrade: true, // write back to disk
})

console.log(upgraded) // { 'react': '^18.3.1', 'react-dom': '^18.3.1' }

Run it directly with Node:

node ./scripts/check-deps.ts

Recommended workflows

Safest upgrade path

1. Ensure the working tree is committed.
2. Run ncu --cooldown 7 to skip recently published versions.
3. Run ncu -u to write updates.
4. Run npm install (or the equivalent for the active package manager).
5. Run the test suite and commit if green.

Detect breaking upgrades automatically

ncu --doctor -u

Reverts broken upgrades one at a time and prints the offender.

Monorepos

# All workspaces, including the root.
ncu -uw

# All packages.json files under the cwd.
ncu --deep -u

# A specific glob, merging root config.
ncu --packageFile 'packages/*/package.json' --mergeConfig -u

Custom registry / private mirror

ncu --registry https://npm.example.com --packageManager npm

# Or a static JSON catalog hosted anywhere.
ncu --registry https://example.com/versions.json --registryType json

Pitfalls and gotchas

• ncu only writes package.json. Lockfile and node_modules updates require a separate install step.
• --doctor modifies the lockfile and node_modules. Use a clean tree.
• The default CLI name ncu collides with ncu-weather-cli and Nvidia CUDA's ncu on some systems. Fall back to npm-check-updates if output is unexpected.
• On Windows, prefer --packageFile package.json if ncu appears to hang. It is sometimes waiting for stdin.
• The cooldown value is read from min-release-age (npm), npmMinimalAgeGate (yarn), or pnpm-workspace.yaml's minimumReleaseAge (pnpm) when --cooldown is not given.
• Pure ESM since v21.0.0. .ncurc.js must be ESM (export default); CJS configs need .cjs extension.
• --format cooldown requires registry time data. Some mirrors do not expose it. Use a public registry if nothing is reported.

Verification cheatsheet

# Show all CLI options.
ncu --help

# Extended help for a single flag.
ncu --help --filter
ncu --help --target
ncu --help --cooldown
ncu --help --doctor