How do I get the number of online players in a Minecraft server from outside the client?

Question

I know that the Minecraft client can query the server for number of players and maximum players, even when the server properties has enable-query set to false, but how do I do this outside of the client? I am trying to implement this as part of a mobile (Android) app.

Answer 1

This is actually quite well-detailed at this page. Please note that I am going to detail the common protocol introduced in version 1.7. Additionally, a new protocol was introduced in 1.9pre4 that contains additional information not found in the previous protocol. Let me detail how to get the basic server information in 1.7+:

1. Send a "handshake" packet with the layout:

   • 0x00 (Packet ID)
   • 0x04 (Protocol Version)
   • Length of server address. This is a VarInt, which means that it has a variable length. The last bit of each byte that would normally indicate the sign instead indicates if the next byte is part of the VarInt.
   • Server address (Host Name or IP Address)
   • Server port (as a Short, Big-endian)
   • 0x01 (Next State)

2. Send a blank "Status Request" packet with the layout:

   • 0x00 (Packet ID)

3. Reading the response, you will get a JSON-encoded object with the following format:

   • Version
     1. Name
     2. Protocol
   • Players
     1. Max
     2. Online
     3. Sample
   • Description
     1. Text
   • Favicon
     1. Mime-type;encoding,

Since you are writing this for Android, I presume you are using Java. Luckily for you, there is already an open-source Java project that details these steps already made for you. Even better, it shows proper use of VarInt when formatting your packets.