# defineSocketContract

> Documentation for Redweb 0.13.3. Install that exact version when following these examples.

One shared Standard Schema contract validates wire payloads and infers client/server types. Route URLs choose the service; individual handler factories dispatch by message type.

## Explain it like I’m five

A socket contract is a shared form for both sides of a conversation. It says which messages exist and what each message must contain, so the server checks a message before handing it to the matching handler.

## When should I use it?

Use it when a site, app, or game client should share payload types and runtime validation with a routed Redweb service.

## Follow the example

This source is part of the [complete socket recipe](/docs/reference/0.13.3/recipes/socket.md). Follow its setup and tests.

```ts
import { defineSocketContract } from 'redweb/contract';
import { z } from 'zod';

const position = { x: z.number().int().min(-100).max(100), y: z.number().int().min(-100).max(100) };

// Share this module with a browser or Node client. It imports no server application code.
export const match = defineSocketContract('1', {
    join: z.object({ name: z.string().trim().min(1).max(40) }).strict(),
    move: z.object(position).strict(),
    resume: z.object({ session: z.string().uuid() }).strict(),
    state: z.object({ session: z.string().uuid(), name: z.string(), ...position }).strict(),
});
```

1. The shared module defines join, move, resume, and state payload schemas once.
2. The match route registers separate handlers created by the contract instead of switching on a secondary action field.
3. The client and server validate their outgoing messages and parse incoming envelopes against the same schema.

## Methods and members

### defineSocketContract(version, schemas, options?)

Creates an immutable contract and negotiated protocol policy from Standard Schema validators. Redweb does not require a particular validator at runtime.

### handler(type, callback)

Creates a BaseHandler subclass. Validation completes before the callback receives its typed payload.

### client(socket)

Wraps an existing WebSocket with typed, validated send and parse methods. It does not open or reconnect the connection.

### send(socket, type, payload, metadata?)

Validates server output before sending through the normal transport and protocol policy.

## What should I watch for?

Schema validation is not authentication or game-rule validation. Keep bearer session IDs private, apply authorization in handlers, and persist important data outside the starter's bounded in-memory sessions. Async validation deadlines cannot preempt synchronous JavaScript.