What Does online-mode Do on a Minecraft Server?

Direct answer

online-mode=true tells a normal standalone Java server to authenticate connecting players through Minecraft's account authentication flow. For an ordinary internet-facing server, keep it enabled.

The normal setting

online-mode=true

Paper documents that setting this to true checks connecting players against Minecraft's account database and requires a valid account. Setting it to false disables that verification and permits unauthenticated/offline-mode clients, including clients commonly called cracked.

For a normal internet-facing server, keep authentication enabled. If you are intentionally researching offline-mode access, read the dedicated cracked/offline-mode guide first because disabling authentication changes player identity and security.

A timeout is not fixed by disabling authentication

If friends cannot reach the server at all, troubleshoot the server address, firewall, port forwarding, and CGNAT. Changing online-mode does not open a closed network path.

Proxy networks are a special case

Velocity and other proxy architectures can require backend servers to be configured differently because the proxy handles player forwarding and authentication. Follow the proxy's current secure player-forwarding documentation; do not copy a standalone-server setting blindly into a network.

Keep backups before identity-mode changes

Player data is associated with UUIDs. Changing authentication/forwarding architecture incorrectly can make inventories, permissions, or ownership appear to belong to different identities. Treat such changes as a migration and back up first.

Never use authentication changes as a network fix

For a normal public standalone Java server, online-mode=true ensures Minecraft account authentication; it cannot fix a closed port or DNS routing error.
On Velocity, the proxy performs authentication and backend settings depend on secure forwarding configuration. Keep the backend inaccessible to the public; do not expose an offline-mode backend.
Back up playerdata and permission stores before identity-mode migrations because incorrect UUID handling can make inventories and permissions appear to disappear.

Official references

These references were checked while preparing this guide. Version-specific behavior can change, so use the project documentation for your exact release when a detail differs.

PaperMC: server.properties reference

Was this article helpful?

Help us improve this article

Tell us what is missing, unclear, outdated, or incorrect. You can also suggest something we should add.