send_formatted_message

Send formatted Slack messages using Block Kit to structure content with interactive elements in specified channels or threads.

Instructions

Send a message with Block Kit formatting

Input Schema

TableJSON Schema

Name	Required	Description
`channel`	Yes	Channel ID
`text`	Yes	Fallback text
`blocks`	Yes	Block Kit blocks array
`thread_ts`	No	Optional thread timestamp to reply to

Implementation Reference

src/tools/messages.ts:103-121 (handler)

The core handler function for the 'send_formatted_message' tool. It validates input using Zod schema, then uses the Slack client to post a message with Block Kit blocks support.

export async function sendFormattedMessage(client: SlackClientWrapper, args: unknown) {
  const params = sendFormattedMessageSchema.parse(args);

  return await client.safeCall(async () => {
    const result = await client.getClient().chat.postMessage({
      channel: params.channel,
      text: params.text,
      blocks: params.blocks as any,
      thread_ts: params.thread_ts,
    });

    return {
      ok: true,
      channel: result.channel,
      ts: result.ts,
      message: result.message,
    };
  });
}

src/utils/validators.ts:78-83 (schema)

Zod schema used for input validation in the handler, defining parameters: channel, text, blocks (array), optional thread_ts.

export const sendFormattedMessageSchema = z.object({
  channel: channelIdSchema,
  text: z.string().min(1),
  blocks: blocksArraySchema,
  thread_ts: timestampSchema.optional(),
});

src/index.ts:291-316 (registration)

Tool metadata registration including name, description, and JSON inputSchema for the MCP list_tools endpoint.

{
  name: 'send_formatted_message',
  description: 'Send a message with Block Kit formatting',
  inputSchema: {
    type: 'object',
    properties: {
      channel: {
        type: 'string',
        description: 'Channel ID',
      },
      text: {
        type: 'string',
        description: 'Fallback text',
      },
      blocks: {
        type: 'array',
        description: 'Block Kit blocks array',
      },
      thread_ts: {
        type: 'string',
        description: 'Optional thread timestamp to reply to',
      },
    },
    required: ['channel', 'text', 'blocks'],
  },
},

src/index.ts:431-431 (registration)
Binds the tool name to the imported handler function from messageTools for the MCP call_tool handler.
```
send_formatted_message: (args) => messageTools.sendFormattedMessage(slackClient, args),
```

Slack MCP Server