How to Use Discord Webhook to Forward Slack Messages With Format Conversion

You have a Slack workspace where your team posts important messages, but you want those messages to appear in a Discord channel with proper formatting. Discord webhooks can receive data from Slack, but the message format differs between the two platforms. Slack uses its own message formatting with features like user mentions, channel links, and rich attachments, while Discord expects a different JSON structure. This article explains how to set up a Discord webhook, configure Slack to send messages to it, and convert Slack message formatting to Discord-compatible formatting using a simple script or middleware.

How Discord Webhooks Work With Slack Messages

A Discord webhook is a simple HTTP endpoint that accepts JSON payloads and posts them to a specified Discord channel. Slack can send messages to any HTTP endpoint using its Outgoing Webhooks feature or Slack Workflows. However, the JSON structure Slack sends differs from what Discord expects. Discord webhooks expect a payload with fields like content, embeds, username, and avatar_url. Slack sends fields like text, user_name, channel_name, and attachments. Without conversion, Slack messages appear as plain text or fail to post entirely.

Prerequisites

Before starting, you need a Discord server where you have the Manage Webhooks permission, a Slack workspace where you can create Outgoing Webhooks or Workflows, and a way to run a serverless function or a small script. This article uses a free Google Cloud Function as the middleware, but you can use any HTTP endpoint you control, such as an AWS Lambda, Azure Function, or a Node.js server on a Raspberry Pi.

Understanding the Format Differences

Slack sends messages in a JSON object that includes the message text, the user who sent it, the channel, and optional attachments. Discord webhooks accept a JSON object with content for plain text, embeds for rich cards, and allowed_mentions for controlling mentions. Key differences include:

• Slack uses text for the message body; Discord uses content.
• Slack uses user_name for the sender name; Discord uses username in the webhook payload.
• Slack supports @user and #channel mentions; Discord uses <@user_id> and <#channel_id>.
• Slack attachments contain title, text, color, and fields; Discord embeds contain title, description, color, and fields.

Steps to Set Up Discord Webhook and Forward Slack Messages

1. Create a Discord Webhook
   Open Discord and go to your server. Click Server Settings > Integrations > Webhooks. Click New Webhook. Give it a name, select the target channel, and click Copy Webhook URL. Save this URL for later.
2. Set Up Slack Outgoing Webhook
   In Slack, go to Slack API dashboard at api.slack.com/apps. Create a new app or use an existing one. Under Features, click Incoming Webhooks and activate them. Or use Outgoing Webhooks under the same app. For Outgoing Webhooks, set the URL to the middleware endpoint you will create in the next step. If you use Slack Workflows, create a new workflow with a Webhook Request trigger and set the URL to your middleware endpoint.
3. Create the Format Conversion Middleware
   Write a simple HTTP endpoint that receives Slack payloads, converts them to Discord format, and forwards them. Example using Node.js and Google Cloud Functions:

   exports.slackToDiscord = (req, res) => {
     const slackPayload = req.body;
     const discordPayload = {
       content: slackPayload.text || '',
       username: slackPayload.user_name || 'Slack User',
       avatar_url: slackPayload.user_icon || 'https://example.com/default-icon.png',
       embeds: []
     };
     if (slackPayload.attachments) {
       slackPayload.attachments.forEach(att => {
         discordPayload.embeds.push({
           title: att.title || '',
           description: att.text || att.fallback || '',
           color: att.color ? parseInt(att.color, 16) : 0,
           fields: att.fields ? att.fields.map(f => ({name: f.title, value: f.value, inline: f.short})) : []
         });
       });
     }
     fetch(DISCORD_WEBHOOK_URL, {
       method: 'POST',
       headers: {'Content-Type': 'application/json'},
       body: JSON.stringify(discordPayload)
     });
     res.status(200).send('OK');
   };

   Deploy this function to Google Cloud Functions, AWS Lambda, or any HTTP endpoint. Set the environment variable DISCORD_WEBHOOK_URL to the URL you copied in step 1.

4. Test the Integration
   In Slack, send a message that includes text, an attachment, or a link. The message should appear in your Discord channel within seconds. Check the Discord channel for the formatted message. If it does not appear, check the logs of your middleware function for errors.
5. Handle Slack Mentions and Channel References
   Slack uses <@U12345> for user mentions and <#C12345> for channel references. Discord uses <@123456789> and <#123456789> with numeric IDs. Write a conversion function that maps Slack user IDs to Discord user IDs if you need mentions to work. For simple forwarding, you can strip the mention syntax or replace it with the user display name from a lookup table.

Common Issues and How to Fix Them

Slack Message Does Not Appear in Discord

Check the middleware function logs. Common causes include incorrect Discord webhook URL, missing environment variable, or the middleware returning an error. Ensure your middleware function returns a 200 status to Slack; otherwise Slack may retry and cause duplicates.

Formatting Looks Wrong in Discord

Slack attachments and Discord embeds have slightly different field names. Map Slack text to Discord description, Slack color (hex string) to Discord color (integer), and Slack fields[].title to Discord fields[].name. Also, Discord embeds have a limit of 6000 characters total; truncate long Slack messages.

User Names Not Showing Correctly

Slack sends user_name as the display name. Discord webhooks accept a username field in the root payload. If you want the Slack user icon, include the avatar_url field. Note that Discord webhooks ignore the username field if you set it to a bot name that violates Discord’s terms.

Discord Webhook vs Slack Webhook: Key Differences

Item	Discord Webhook	Slack Webhook
Payload format	JSON with content, embeds, username, avatar_url	JSON with text, attachments, channel, username, icon_url
Mention syntax	<@user_id> or <@&role_id>	<@user_id> or <!subteam^group_id>
Attachment support	Embeds with title, description, fields, color, image, footer	Attachments with title, text, fields, color, image_url, thumb_url
Rate limits	30 requests per second per webhook	1 message per second per webhook
Custom username	Yes, set in payload	Yes, set in payload

After setting up the middleware, you can forward Slack messages to Discord with proper formatting. The conversion script handles text, attachments, and user names. For advanced use, extend the script to map Slack user mentions to Discord user IDs using a lookup table. This integration keeps your team in sync across both platforms without manual reposting.