Labels

Labels are key-value pairs attached to events. Hook0 uses them to route events to the right subscriptions. You can use labels for multi-tenancy, environment separation, or any filtering logic you need.

Key points

• Every event must include at least one label
• Subscriptions filter events by matching label values
• Labels are how you implement multi-tenant routing
• Matching is case-sensitive and exact

Minimum Requirement

Every event must include at least one label. The API rejects events with empty labels.

How labels work

Matching rules

• A subscription receives an event only if all its label filters match the event's labels
• If an event lacks a label that the subscription filters on, the event is not delivered
• Subscriptions can have fewer labels than events (partial matching)
• Label values are case-sensitive and must match exactly

Common patterns

Pattern	Example label	Purpose
Multi-tenancy	tenant_id: "acme_corp"	Isolate events per customer
Environment	environment: "production"	Separate prod/staging/dev
Priority	priority: "critical"	Route urgent events differently
Geographic	region: "eu-west-1"	Route by location
Source	source: "mobile_app"	Identify event origin

Naming conventions

• Use snake_case for keys: tenant_id, event_source
• Be descriptive: payment_provider not pp
• Avoid sensitive data: never use password, ssn, credit_card
• Use consistent naming across all events

What's next?

• Events - Attach labels to events
• Subscriptions - Filter events with labels
• Event Types - Categorize your events
• Applications - Manage labels per application