What does "npm ERR! code E406 npm ERR! 406 Not Acceptable" mean?

HTTP 406 Not Acceptable is a client error response that indicates the server has received your request and the resource exists, but it cannot provide a response matching the content type your npm client is requesting. This typically happens when: 1. install-v1+json) that the registry server doesn't understand or support.

What causes "npm ERR! code E406 npm ERR! 406 Not Acceptable"?

Custom registry (Artifactory, Nexus, GitLab, etc.) doesn't support the Accept headers npm sends Registry URL is incorrectly configured - missing API path or using wrong protocol Private registry doesn't fully implement npm registry specification and fails content negotiation

Is the "npm ERR! code E406 npm ERR! 406 Not Acceptable" error serious?

Yes. This is a high-severity error that usually blocks work until it is fixed, but the steps above resolve it.

How to fix npm ERR! code E406 npm ERR! 406 Not Acceptable in npm

npmINTERMEDIATEHIGHLast verified Dec 5, 2025· 21 views

The npm E406 error occurs when the npm registry server rejects your request due to incompatible Accept headers or misconfigured registry settings. This commonly happens with custom registries like Artifactory, Nexus, or private repositories.

Quick fix

Fixes npm ERR! code E406 npm ERR! 406 Not Acceptable

npm config get registry

Verify your current registry configuration
Validate the registry URL format
Clear npm cache and retry
Reset to default registry and test

npm — error

$npm config get registry
npm ERR! code E406
npm ERR! 406 Not Acceptable

How to fix "npm ERR! code E406 npm ERR! 406 Not Acceptable"

1Verify your current registry configuration

First, check which registry npm is currently configured to use:

bash

npm config get registry

If you see a custom registry URL (not https://registry.npmjs.org/), that's likely where the issue is. Take note of the full URL for the next steps.

2Validate the registry URL format

Ensure your registry URL follows the correct format:

For Artifactory:

bash

npm config set registry https://artifacts.company.com/artifactory/api/npm/npm-remote/

For Nexus 3:

bash

npm config set registry https://nexus.company.com/repository/npm/

For GitLab:

bash

npm config set registry https://gitlab.company.com/api/v4/packages/npm/

The key is including the /api/ or /repository/ path that points to the npm proxy/repository.

3Clear npm cache and retry

Clear any cached data that might be causing issues:

bash

npm cache clean --force

Then attempt your install again:

bash

npm install

This removes stale cache entries that might be interfering with content negotiation.

4Reset to default registry and test

Temporarily switch to the official npm registry to isolate the problem:

bash

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

If this succeeds, the issue is with your custom registry configuration. If it fails, the problem is elsewhere (network, authentication, etc.). Once confirmed, switch back to your custom registry and check the URL format from Step 2.

5Fix protocol or authentication issues

For GitHub dependencies in package.json, use the git:// protocol instead of https://:

json

{
  "dependencies": {
    "my-package": "git://github.com/user/repo.git#branch-name"
  }
}

For private registries requiring authentication, ensure your .npmrc has the correct credentials:

bash

npm login --registry=https://artifacts.company.com/artifactory/api/npm/npm-remote/

Or add to .npmrc:

bash

@myorg:registry=https://artifacts.company.com/artifactory/api/npm/npm-remote/
//artifacts.company.com/artifactory/api/npm/npm-remote/:_authToken=YOUR_TOKEN_HERE

How to fix npm ERR! code E406 npm ERR! 406 Not Acceptable in npm

Quick fix

What this error means

Typical symptoms

Common causes