Slack bot

Time to complete: 10 minutes

This guide walks you through building a Slack bot that responds to mentions in channels.

If you just want to send simple Slack messages without interactivity, check out our Slack webhook guide. And if you want an AI agent Slack bot, see our Slack agent guide.

Step 1: Remix the bot template

Remix this val to get started:

View and run this example on Val Town

export const slackReplyToMessage = async (req: Request) => {
  // Handle different request methods
  if (req.method === "GET") {
    return new Response("Slack bot is running!", { status: 200 });
  }

  // Parse JSON body safely
  let body;
  try {
    const text = await req.text();
    if (!text) {
      return new Response("Empty request body", { status: 400 });
    }
    body = JSON.parse(text);
  } catch (error) {
    console.error("JSON parsing error:", error);
    return new Response("Invalid JSON", { status: 400 });
  }

  // Verify the request is genuine
  if (body.token !== Deno.env.get("slackVerificationToken")) {
    return new Response(undefined, { status: 401 });
  }

  // Respond to the initial challenge (when events are enabled)
  if (body.challenge) {
    return Response.json({ challenge: body.challenge });
  }

  // Reply to app_mention events
  if (body.event?.type === "app_mention") {
    try {
      const result = await fetch("https://slack.com/api/chat.postMessage", {
        method: "POST",
        headers: {
          "Authorization": `Bearer ${Deno.env.get("slackToken")}`,
          "Content-Type": "application/json",
        },
        body: JSON.stringify({
          channel: body.event.channel,
          thread_ts: body.event.ts,
          text: "Hello, ~World~ from Val Town!",
        }),
      });

      const responseData = await result.json();
      console.log(responseData);

      // Return proper response to acknowledge receipt
      return new Response(undefined, { status: 200 });
    } catch (error) {
      console.error("Error posting to Slack:", error);
      return new Response(undefined, { status: 500 });
    }
  }

  // Return 200 for other event types
  return new Response(undefined, { status: 200 });
};