Launcher Setup

What this covers

This page explains what address to put into launchers and servers. For protocol details, read Launcher Login and Yggdrasil API.

Get the Correct Address

Administrators should give players a public site URL, for example:

https://skin.example.com

The Yggdrasil API root is usually:

https://skin.example.com/api/yggdrasil

If the launcher supports API Location Indication, enter the site root. AsterYggdrasil serves this header from the homepage:

X-Authlib-Injector-API-Location: /api/yggdrasil/

If the launcher does not support ALI, enter the full /api/yggdrasil address.

Before Players Log In

Players need at least:

• A site account.
• The site account password.
• A Minecraft profile under that account.

If the account has no Minecraft profile, launcher login may succeed but there is no usable selectedProfile for joining servers. Create a profile on the site first.

Quick Launcher Reference

Launcher capability	What to enter
Supports ALI	https://skin.example.com
Does not support ALI	https://skin.example.com/api/yggdrasil
Needs account identifier	Site account username or email
Allows profile-name login	Only after admin enables yggdrasil_allow_profile_name_login

Launcher UI labels vary. Common names include "auth server", "Yggdrasil API", "third-party login", or "authlib-injector server". They all point to the same protocol root.

javaagent Form

If you use authlib-injector directly as a javaagent:

-javaagent:authlib-injector.jar=https://skin.example.com/api/yggdrasil

Servers should stay in online mode:

online-mode=true
enforce-secure-profile=true

If you temporarily disable secure profile checks, review the impact first. Troubleshooting-only settings should not remain in production configuration.

Check After Login

After successful login, the launcher should receive:

• accessToken
• clientToken
• availableProfiles
• selectedProfile

If login succeeds but joining fails, read Troubleshooting.

If joining works but skins do not show, read Troubleshooting.