Poképon uses a couple of custom application-layer protocols to communicate between the client and the server.

The main protocol used is one called JACK (Java Awful Client-server Kit), which is a really basic line-oriented text protocol. A typical message will look like this:

!word [tokens...]

Here, the leading ! specifies the message type, word specifies the message, and tokens is an optional blank-separated list of strings which may be used as arguments for the word message.

Poképon uses the following message types:

  • A message starting with ! is a communication message
  • A message starting with / is a command
  • A message starting with ~ is a battle message
  • Any other message is a simple message

(This distinction is made by the Server’s and Client’s Connection Executors, which are the classes that parse the incoming messages read from the socket.)


The connection between the client and the server is set up by a “handshake” that has the basic function to reject connections which surely aren’t coming from Pokepon clients (one may easily write a client complying with the Poképon protocol, though).

As soon as a connection is received, the server sends a !youros message, to which the client responds with a !myos <arg> message. <arg> is supposed to be the OS the client is running atop, but no validation is made by the server, so it can be virtually any string.

If the client succeeds in sending the !myos message, the server accepts its connection and broadcasts its name to other clients.

The client also needs to respond any !ping message from the server with a !pong message, or the server will kick it out after the ping times out.

Battle messages

During battles, the client and the server communicate via a Pokémon Showdown-like protocol wrapped into the JACK protocol.

More specifically, client and server send messages like:

~id |type|data

where id is the id of the battle this message refers to, and the following tokens are interpreted as a battle command.

A battle command has the syntax |type[|token1|token2|...]. These have almost the same semantics as the JACK messages (word + list-of-tokens), the only differences being: 1. tokens are separated by |, not whitespace 2. there are no different “message types”

All these commands are interpreted by the BattleTask (on the Server) and the BattlePanel (on the Client).