What This Error Means
npm connected over HTTPS, but the certificate presented by the server does not match the registry hostname you requested.
How to Fix It
Confirm which registry host npm is calling:npm config get registry
Check system time and timezone (NTP). If it's wrong, fix it and retry.
Check for proxy settings:npm config get proxy and npm config get https-proxy
Check TLS config:npm config get strict-ssl and npm config get cafile
If you use scoped registries, verify .npmrc mapping (example: @your-scope:registry=...).
If you use a private registry, ensure the certificate includes the exact hostname you use in .npmrc.
If you control the registry/proxy, ensure it serves the full certificate chain (leaf + intermediates).
Inspect the served chain:openssl s_client -showcerts -connect <host>:443 -servername <host> </dev/null
Proper fix:trust the CA that is signing the certificate chain.
If you are behind a corporate TLS proxy, export the corporate root CA and configure npm:npm config set cafile /path/to/corp-ca.pem
In CI, prefer NODE_EXTRA_CA_CERTS=/path/to/corp-ca.pem so Node trusts the internal CA without changing global npm config.
Temporary diagnostics only:if you must confirm a trust issue, run npm --strict-ssl=false <command> once, then restore validation immediately.
Do not leave strict-ssl=false or NODE_TLS_REJECT_UNAUTHORIZED=0 in CI, shell profiles, or checked-in config. They disable certificate validation and increase MITM risk.
If you changed npm config for a one-off test, revert it immediately:npm config set strict-ssl true and unset NODE_TLS_REJECT_UNAUTHORIZED
Retry with npm --verbose and keep the full output for troubleshooting.
Why It Happens
The registry hostname does not match the certificate (CN/SAN mismatch).
A proxy is presenting a certificate for a different hostname.
You are hitting the wrong registry host due to .npmrc scope mapping or an env override.
How to Verify
Run npm ping and confirm it succeeds.
Re-run the original command and confirm HOSTNAME_MISMATCH is gone.
Manual certificate validation
Inspect SANs for the registry cert:openssl s_client -connect <host>:443 -servername <host> </dev/null | openssl x509 -noout -text
Confirm the hostname appears under Subject Alternative Name (SAN).
If you do a one-off SSL-bypass test, restore certificate validation immediately after it.
Examples
npm ERR! code HOSTNAME_MISMATCHHow npm verifies TLS certificates
npm uses Node.js for HTTPS. Node verifies the certificate chain and checks that the certificate matches the hostname you requested.
If the hostname does not match, the connection is rejected even if the certificate is otherwise trusted.
Prevention Tips
Avoid registry host aliases that do not match the deployed certificate.
Keep .npmrc scope mappings explicit and reviewed.
Where This Can Be Triggered
github.com/npm/cli/blob/417daa72b09c5129e7390cd12743ef31bf3ddb83/lib/utils/ping.js
This is the registry request path where npm talks to the network. DNS/TLS errors like this code are raised by Node/OS during this request. - GitHub
// used by the ping and doctor commands
const npmFetch = require('npm-registry-fetch')
module.exports = async (flatOptions) => {
const res = await npmFetch('/-/ping', { ...flatOptions, cache: false })
return res.json().catch(() => ({}))
}