How to fix npm ERR! code E400 npm ERR! 400 Bad Request in npm

Check your current registry configuration and ensure it's pointing to the official npm registry.

npm config get registry

npm config set registry https://registry.npmjs.org/

npm config get registry

If you intentionally use a private registry, verify the URL is correct and accessible.

Corrupted cache or cached authentication tokens can cause the registry to reject requests.

npm cache clean --force

rm -rf node_modules package-lock.json

npm install

This forces npm to fetch fresh metadata and cache from the registry.

An E400 error when publishing often means your package.json has invalid syntax or fields. Validate the JSON and check critical fields.

cat package.json | jq .

npm ls

Ensure your package.json contains:
- Valid JSON syntax (no trailing commas, proper quotes)
- Valid package name (lowercase, no spaces, only hyphens/underscores for separators)
- Valid version (semantic versioning: major.minor.patch)
- If publishing to a scoped registry: scope matches your organization

If you're publishing a scoped package, ensure the scope matches your registry organization.

cat ~/.npmrc

# For Nexus, publish to hosted repo (not group):
npm publish --registry https://your-nexus.com/repository/npm-hosted/

For multiple registries in .npmrc:

@myorg:registry=https://private-registry.com/
@otherorg:registry=https://another-registry.com/

Network configuration, proxies, or stale authentication can cause requests to be rejected.

npm config set proxy http://proxy.company.com:8080
npm config set https-proxy http://proxy.company.com:8080

npm login

npm config list

If using a VPN, ensure it's active and the registry is accessible.