Channels

Channels are the destinations where Alphorn delivers notifications. Each channel connects to an external service - a Slack workspace, an email address, a push notification service, etc.

Supported ChannelsCopy Anchor Link

Chat & MessagingCopy Anchor Link

EmailCopy Anchor Link

Push NotificationsCopy Anchor Link

SMSCopy Anchor Link

Incident ManagementCopy Anchor Link

Custom IntegrationsCopy Anchor Link

Adding a ChannelCopy Anchor Link

1. Navigate to Channels in the dashboard
2. Click Add channel
3. Select the channel type
4. Enter the required configuration - each channel type shows a setup guide in the form
5. Send a test notification to verify (admins and owners; not available for Live Stream)
6. Link the channel to a webhook - on the webhook page, select it in the channel list

A channel only receives notifications from webhooks it is linked to. You can link one channel to many webhooks, each with its own filter.

Disabling and Deleting ChannelsCopy Anchor Link

• A disabled channel receives no new notifications, and pending retries for it are dropped. It still counts toward your plan's channel limit.
• Deleting a channel removes it from all webhooks. Its delivery history stays visible under Messages, and it no longer counts toward your plan's channel limit.

Send Rate LimitsCopy Anchor Link

To stay within the services' own limits, Alphorn sends at most 60 messages per minute to a Slack channel, 50 to a Discord channel, and 20 to a Telegram channel. Extra deliveries wait for the next minute without using up a retry - see Retries → Per-Channel Throttling.

Message Length LimitsCopy Anchor Link

Incoming titles are cut to 200 characters and messages to 4,000 characters. Some services have lower limits, so Alphorn shortens the text to fit each one before sending (longer text ends with …):

Email and Opsgenie need a subject or title line: they use the notification title, or the first line of the message (up to 100 characters) when there is no title. PagerDuty gets Title: message as its summary, cut to 1,024 characters.

Priority MappingCopy Anchor Link

Channels with their own priority or severity levels get the notification priority mapped onto their scale:

Notifications without a priority use the channel's default: default for ntfy, 5 for Gotify, 0 for Pushover, and the Default Severity / Default Priority you configured for PagerDuty and Opsgenie.

Channel LimitsCopy Anchor Link

Channel availability depends on your plan:

Generic WebhookCopy Anchor Link

The Webhook channel lets you send notifications to any HTTP endpoint. Use it to integrate with services that Alphorn doesn't have a dedicated channel for.

Alphorn sends a JSON body:

{
  "title": "Notification title",
  "message": "Notification body",
  "priority": 3,
  "tags": ["tag1", "tag2"],
  "payload": { "the": "original JSON request body" },
  "timestamp": "2025-01-15T10:30:00.000Z"
}

• message and timestamp are always present
• title, priority, and tags are left out when the notification doesn't have them
• payload is the original JSON request body that came into the Alphorn webhook, nested under its own key. For plain-text notifications it is an empty object ({})
• The test button sends a different body - {"title", "body", "timestamp", "_test": true} - so your receiver can tell test pings apart

The request also carries a signed X-Alphorn-Trace header (other URL-based channels like Slack, Teams, Matrix, or ntfy send it too). Alphorn uses it to detect loops when a channel points at another Alphorn webhook; after 3 hops (WEBHOOK_MAX_HOPS when self-hosting), or when the notification comes back to a webhook it already passed, the request is rejected with 508. The header is signed with BETTER_AUTH_SECRET, so loops across two self-hosted instances are only detected when both use the same secret.