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Pokémon Showdown’s protocol is a newline-and-pipe-delimited text stream that enables communication between clients and servers, as well as battle simulation.

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Connection Methods

Pokémon Showdown is implemented using SockJS, a compatibility layer over raw WebSocket. You can connect directly using WebSocket: 
ws://sim.smogon.com:8000/showdown/websocket
or with SSL: 
wss://sim3.psim.us/showdown/websocket

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Protocol Structure

Client-to-Server

Messages sent from clients to the server follow a simple ROOMID|TEXT format

Server-to-Client

Messages from the server include room identifiers and pipe-delimited data blocks

Battle Protocol

Battle-specific messages use a specialized format for game state updates

Choice Requests

JSON-based requests for player decisions during battles

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Message Format Basics

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Server Messages

Server-to-client messages follow this structure: 
>ROOMID
MESSAGE
MESSAGE
MESSAGE
...
The >ROOMID line can be omitted if the room is lobby or global. Empty lines should be ignored.
Most messages start with | and follow the pattern: 
|TYPE|DATA

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Client Messages

Messages from clients to the server use: 
ROOMID|TEXT
ROOMID can be left blank if unneeded. Responses will be sent to a PM box with no username.
TEXT can contain newlines, which will be treated as if each line were sent separately.

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Message Type Abbreviations

For bandwidth efficiency, five common message types are abbreviated:
Full TypeAbbreviatedDescription
chatcChat messages
joinjUser joined
leavelUser left
namenName change
battlebBattle started
Uppercase versions (J, L, N, B) indicate high-frequency events that clients may want to suppress from inline display.

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Example Message Flow

Here’s what a typical chat room interaction looks like: 
|j| Some dude
|c|@Moderator|hi!
|c| Some dude|you suck and i hate you!
Some dude was banned by Moderator.
|l| Some dude
|b|battle-ou-12| Cool guy|@Moderator
This might be displayed as: 
Some dude joined.
@Moderator: hi!
Some dude: you suck and i hate you!
Some dude was banned by Moderator.
Some dude left.
OU battle started between Cool guy and Moderator

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Debugging

The official client logs protocol messages in the JavaScript console (F12 in most browsers), which helps understand what’s happening during gameplay.

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Client Implementations

Reference implementations are available in multiple languages:

Official Client

HTML5 + JavaScript implementationView on GitHub

Android Client

Kotlin/Java implementation by MajeurView on GitHub

Node.js Bot

Chat bot by Quinella and TalkTakesTimeView on GitHub

Ruby Bot

Chat bot by pickdenisView on GitHub

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Next Steps

Client-Server Messages

Learn about room messages, authentication, and server commands

Battle Protocol

Understand battle-specific messages and game state updates

Choice Requests

Handle player decisions and move selections

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