VRChat MCP OSC

Instructions

Implementation Reference

• packages/mcp-server/src/server.ts:599-621 (registration)

  MCP tool registration for 'send_message', including inline schema (Zod) and handler function that delegates to inputTools.sendChatboxMessage

  server.tool(
    'send_message',
    'Send a message to the VRChat chatbox.',
    {
      message: z.string().describe('Message to send'),
      send_immediately: z.boolean().default(true).describe('Send immediately or just populate chatbox')
    },
    async ({ message, send_immediately }, extra) => {
      try {
        const ctx = createToolContext(extra);
        const result = await inputTools.sendChatboxMessage(message, send_immediately, ctx);
        return { content: [{ type: 'text', text: result }] };
      } catch (error) {
        return { 
          content: [{ 
            type: 'text', 
            text: `Error sending message: ${error instanceof Error ? error.message : String(error)}` 
          }],
          isError: true
        };
      }
    }
  );

• packages/mcp-server/src/tools/inputTools.ts:406-427 (handler)

  Core handler logic in InputTools.sendChatboxMessage, wraps wsClient call and provides user feedback

  public async sendChatboxMessage(
    message: string,
    sendImmediately: boolean = true,
    ctx?: ToolContext
  ): Promise<string> {
    if (ctx) {
      await ctx.info(`Sending message: "${message}" (immediate: ${sendImmediately})`);
    }
  
    try {
      const success = await this.wsClient.sendChatboxMessage(message, sendImmediately);
      if (success) {
        return `Message sent: "${message}"`;
      } else {
        return `Failed to send message: "${message}"`;
      }
    } catch (error) {
      const errorMsg = `Error sending message: ${error instanceof Error ? error.message : String(error)}`;
      logger.error(errorMsg);
      return errorMsg;
    }
  }

• packages/mcp-server/src/ws-client.ts:590-602 (helper)

  WebSocket client method that sends 'chatbox/sendMessage' RPC to relay server

  public async sendChatboxMessage(
    message: string,
    sendImmediately: boolean = true,
    notification: boolean = true
  ): Promise<boolean> {
    const response = await this.sendRequest<{ success: boolean }>('chatbox/sendMessage', {
      message,
      immediate: sendImmediately,
      notification
    });
    this.logger.info(`Chatbox message response: ${JSON.stringify(response)}`);
    return response.success;
  }

• packages/relay-server/src/relay-server.ts:295-307 (handler)

  Relay server RPC handler for 'chatbox/sendMessage' that delegates to oscClient.send_chatbox

  case 'chatbox/sendMessage':
    // Send a chatbox message
    const message = data.message as string;
    const sendImmediately = data.immediate as boolean ?? true;
    const notification = data.notification as boolean ?? true;
  
    if (!message) {
      response.error = { message: 'Missing message text' };
    } else {
      const result = this.oscClient.send_chatbox(message, sendImmediately, notification);
      response.data = { success: result };
    }
    break;