feat(slack-advanced): add send_channel_message tool

packages/slack-advanced/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@arvoretech/slack-advanced-mcp",
-  "version": "1.0.0",
+  "version": "1.1.0",
   "description": "Advanced Slack MCP Server with semantic user search, smart DMs, style analysis, thread extraction, audio transcription, and image analysis",
   "main": "dist/index.js",
   "type": "module",

packages/slack-advanced/src/server.ts

@@ -18,6 +18,7 @@ import {
   TranscribeAudioParamsSchema,
   AnalyzeImageParamsSchema,
   GetFileInfoParamsSchema,
+  SendChannelMessageParamsSchema,
 } from "./types.js";
 
 export class SlackAdvancedMCPServer {
@@ -91,6 +92,15 @@ export class SlackAdvancedMCPServer {
       return this.messagingTools.sendDm(SendDmParamsSchema.parse(params));
     });
 
+    this.server.registerTool("send_channel_message", {
+      title: "Send Channel Message",
+      description:
+        "Send a message to a Slack channel. Accepts channel ID or #channel-name. Supports thread replies and markdown link conversion.",
+      inputSchema: SendChannelMessageParamsSchema.shape,
+    }, async (params) => {
+      return this.messagingTools.sendChannelMessage(SendChannelMessageParamsSchema.parse(params));
+    });
+
     this.server.registerTool("get_dm_history", {
       title: "Get DM History",
       description:

packages/slack-advanced/src/slack-client.ts

@@ -205,6 +205,36 @@ export class SlackClient {
     );
   }
 
+  async resolveChannelId(identifier: string): Promise<string> {
+    if (/^[A-Z0-9]+$/.test(identifier)) {
+      return identifier;
+    }
+
+    const name = identifier.replace(/^#/, "");
+
+    let cursor: string | undefined;
+    do {
+      const params: Record<string, unknown> = { limit: 200, types: "public_channel,private_channel" };
+      if (cursor) params.cursor = cursor;
+
+      const res = await this.request<{
+        ok: boolean;
+        channels: Array<{ id: string; name: string }>;
+        response_metadata?: { next_cursor?: string };
+      }>("conversations.list", params);
+
+      const match = res.channels.find((c) => c.name === name);
+      if (match) return match.id;
+
+      cursor = res.response_metadata?.next_cursor || undefined;
+    } while (cursor);
+
+    throw new SlackAdvancedMCPError(
+      `Could not resolve channel: ${identifier}`,
+      "CHANNEL_NOT_FOUND"
+    );
+  }
+
   async openDm(userId: string): Promise<string> {
     const res = await this.request<{
       ok: boolean;

packages/slack-advanced/src/tools/messaging.ts

@@ -2,6 +2,7 @@ import { SlackClient } from "../slack-client.js";
 import type {
   SendDmParams,
   GetDmHistoryParams,
+  SendChannelMessageParams,
   McpToolResult,
   SlackMessage,
 } from "../types.js";
@@ -82,6 +83,45 @@ export class MessagingTools {
     }
   }
 
+  async sendChannelMessage(params: SendChannelMessageParams): Promise<McpToolResult> {
+    try {
+      const channelId = await this.slack.resolveChannelId(params.channel);
+
+      let text = params.text;
+      if (params.content_type === "text/markdown") {
+        text = this.convertMarkdownLinksToMrkdwn(text);
+      }
+
+      const msgParams: Record<string, unknown> = {
+        channel: channelId,
+        text,
+      };
+
+      if (params.thread_ts) {
+        msgParams.thread_ts = params.thread_ts;
+      }
+
+      const res = await this.slack.request<{
+        ok: boolean;
+        channel: string;
+        ts: string;
+        message: { text: string; ts: string };
+      }>("chat.postMessage", msgParams);
+
+      return this.ok({
+        sent: true,
+        channel: res.channel,
+        ts: res.ts,
+      });
+    } catch (error) {
+      return this.formatError(error);
+    }
+  }
+
+  private convertMarkdownLinksToMrkdwn(text: string): string {
+    return text.replace(/\[([^\]]+)\]\(([^)]+)\)/g, "<$2|$1>");
+  }
+
   private ok(data: unknown): McpToolResult {
     return {
       content: [{ type: "text", text: JSON.stringify(data, null, 2) }],

packages/slack-advanced/src/types.ts

@@ -128,6 +128,25 @@ export const GetFileInfoParamsSchema = z.object({
     .describe("Slack file ID"),
 });
 
+export const SendChannelMessageParamsSchema = z.object({
+  channel: z
+    .string()
+    .min(1, "Channel is required")
+    .describe("Channel ID (e.g. C01EXAMPLE) or channel name (e.g. #general)"),
+  text: z
+    .string()
+    .min(1, "Message text is required")
+    .describe("Message content (supports Slack mrkdwn)"),
+  thread_ts: z
+    .string()
+    .optional()
+    .describe("Thread timestamp to reply in a thread"),
+  content_type: z
+    .enum(["text/plain", "text/markdown"])
+    .optional()
+    .describe("Content type for link formatting. Use text/markdown for [text](url) links"),
+});
+
 export type SearchUsersParams = z.infer<typeof SearchUsersParamsSchema>;
 export type GetUserProfileParams = z.infer<typeof GetUserProfileParamsSchema>;
 export type SendDmParams = z.infer<typeof SendDmParamsSchema>;
@@ -137,6 +156,7 @@ export type GetThreadFromLinkParams = z.infer<typeof GetThreadFromLinkParamsSche
 export type TranscribeAudioParams = z.infer<typeof TranscribeAudioParamsSchema>;
 export type AnalyzeImageParams = z.infer<typeof AnalyzeImageParamsSchema>;
 export type GetFileInfoParams = z.infer<typeof GetFileInfoParamsSchema>;
+export type SendChannelMessageParams = z.infer<typeof SendChannelMessageParamsSchema>;
 
 export type McpTextContent = {
   type: "text";