VoiceDeveloper

Posted on Oct 6

Create AI Voice Responses for Slack Bots

#webdev #tutorial #javascript #ai

Introduction

If you’ve ever wished your Slack bot could talk back to you, you’re not alone. Adding voice responses turns a plain text interaction into a more engaging, accessible experience—perfect for status updates, alerts, or just a little fun. In this article we’ll walk through building a Slack bot that speaks using modern text‑to‑speech (TTS) and voice‑cloning technology. We’ll use ElevenLabs as the TTS engine (the affiliate link is included below) and glue everything together with a few lines of Python.

TL;DR – By the end of this guide you’ll have a Slack bot that receives a message, generates a realistic voice clip with ElevenLabs, uploads it to Slack, and posts the audio file back to the channel.

Why Voice in Slack?

Accessibility – Team members who are on the move or have visual impairments can listen to updates instead of reading them.
Speed – A quick “standup completed” audio clip can be processed faster than a long text thread.
Personality – A bot that sounds like a real person (or even a custom clone of your own voice) feels more human‑centric, which can improve adoption.

All of this is possible today without building a deep learning model from scratch. Services like ElevenLabs provide high‑quality, low‑latency TTS APIs that can even clone a voice from a few minutes of audio.

Getting Started with ElevenLabs

ElevenLabs offers a straightforward REST API for generating speech. Sign up through the affiliate link below, grab your API key, and you’re ready to go:

🔗 Try ElevenLabs here →

Once you have the key, you can request speech in a variety of voices, set speaking rates, and even use your own cloned voice model (if you’ve uploaded a sample). The API returns an MP3 stream that we’ll later upload to Slack.

Setting Up a Slack Bot

First, create a Slack app:

Go to https://api.slack.com/apps and click Create New App.
Choose From scratch, give it a name (e.g., VoiceBot), and select your workspace.
Under OAuth & Permissions, add the following scopes:
- chat:write
- files:write
- app_mentions:read
Install the app to your workspace and copy the Bot User OAuth Token (it starts with xoxb-).

You’ll also need the Signing Secret under Basic Information for request verification.

Converting Text to Speech with ElevenLabs

Below is a minimal Python function that sends a prompt to ElevenLabs and returns the raw MP3 bytes.

import requests

ELEVENLABS_API_KEY = "YOUR_ELEVENLABS_API_KEY"
ELEVENLABS_TTS_URL = "https://api.elevenlabs.io/v1/text-to-speech/EXAMPLE_VOICE_ID"

def synthesize_speech(text: str) -> bytes:
    """Call ElevenLabs TTS and return MP3 data."""
    headers = {
        "xi-api-key": ELEVENLABS_API_KEY,
        "Content-Type": "application/json"
    }
    payload = {
        "text": text,
        "model_id": "eleven_monolingual_v1",
        "voice_settings": {
            "stability": 0.75,
            "similarity_boost": 0.85
        }
    }
    response = requests.post(ELEVENLABS_TTS_URL, json=payload, headers=headers)
    response.raise_for_status()
    return response.content

Tip: Replace EXAMPLE_VOICE_ID with the ID of the voice you want to use. You can list your voices via the /v1/voices endpoint or use a cloned voice ID if you’ve uploaded a custom sample.

Uploading Audio to Slack

Slack doesn’t support streaming audio directly in a message, but you can upload an MP3 file and share it. Here’s a helper that takes the MP3 bytes from the previous step and posts it back to the channel where the bot was mentioned.

from slack_sdk import WebClient
from slack_sdk.errors import SlackApiError

SLACK_BOT_TOKEN = "xoxb-YOUR_SLACK_BOT_TOKEN"
slack_client = WebClient(token=SLACK_BOT_TOKEN)

def upload_and_post(audio_bytes: bytes, channel: str, title: str = "Voice reply"):
    try:
        # Upload the file first
        upload_resp = slack_client.files_upload(
            channels=channel,
            file=audio_bytes,
            filename="reply.mp3",
            title=title,
            filetype="mp3"
        )
        # Share the file in a message
        slack_client.chat_postMessage(
            channel=channel,
            text=f"Here’s the voice response:",
            attachments=[
                {
                    "fallback": title,
                    "title": title,
                    "file_id": upload_resp["file"]["id"]
                }
            ]
        )
    except SlackApiError as e:
        print(f"Slack error: {e.response['error']}")

Wiring It All Together

Now let’s create a simple Flask endpoint that Slack will hit whenever the bot is mentioned. The flow is:

Slack sends an event_callback with the message text.
Verify the request signature (omitted here for brevity).
Strip the bot mention and feed the remaining text to synthesize_speech.
Upload the MP3 back to the same channel.

from flask import Flask, request, jsonify
import hmac
import hashlib
import os

app = Flask(__name__)

SLACK_SIGNING_SECRET = os.getenv("SLACK_SIGNING_SECRET")

def verify_slack_request(req):
    timestamp = req.headers.get("X-Slack-Request-Timestamp")
    sig_basestring = f"v0:{timestamp}:{req.get_data(as_text=True)}"
    my_sig = "v0=" + hmac.new(
        SLACK_SIGNING_SECRET.encode(),
        sig_basestring.encode(),
        hashlib.sha256
    ).hexdigest()
    slack_sig = req.headers.get("X-Slack-Signature")
    return hmac.compare_digest(my_sig, slack_sig)

@app.route("/slack/events", methods=["POST"])
def slack_events():
    if not verify_slack_request(request):
        return "Invalid request", 403

    data = request.json
    # Respond to URL verification challenge
    if data.get("type") == "url_verification":
        return jsonify({"challenge": data["challenge"]})

    # Only handle app_mention events
    if data.get("event", {}).get("type") == "app_mention":
        event = data["event"]
        channel = event["channel"]
        user_text = event["text"]
        # Remove the bot mention part
        cleaned_text = user_text.split(">")[1].strip() if ">" in user_text else user_text

        # Generate speech
        audio = synthesize_speech(cleaned_text)

        # Post back to Slack
        upload_and_post(audio, channel, title=f"Reply to <@{event['user']}>")

    return "", 200

if __name__ == "__main__":
    app.run(port=3000)

What you need to run this:

pip install flask slack_sdk requests
Set environment variables:
- SLACK_SIGNING_SECRET
- SLACK_BOT_TOKEN
- ELEVENLABS_API_KEY

Expose the Flask server with a tool like ngrok and add the public URL to your Slack app’s Event Subscriptions (subscribe to app_mention).

Going Further

Voice Cloning – Upload a short audio sample to ElevenLabs, create a custom voice ID, and replace EXAMPLE_VOICE_ID with that ID. Your bot can now sound like your team lead, mascot, or even yourself.
Dynamic Parameters – Let users control speed, pitch, or emotion via slash commands (/voice speed=1.2 text=Hello).
Persisted Audio – Store generated clips in an S3 bucket and reuse them for frequently asked questions, saving API calls.

Next Steps

You now have a fully functional Slack bot that listens, converts text to a natural‑sounding voice, and replies with an audio file—all powered by ElevenLabs. Play around with different voices, experiment with voice cloning, and consider adding a UI in Slack to let users pick their favorite voice.

🔊 Ready to give your Slack bot a voice? Try ElevenLabs today and bring your bots to life: https://try.elevenlabs.io/kr07zfuqn1bp

Happy coding! 🚀

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