Events Overview

This section covers how you work with events in application development — declaring payloads, naming conventions, dispatching from rules, versioning, and testing.

For the append-only ledger and replay, see Replay and Debugging — Ledger Events.

How events fit into Causet

Events are facts appended to the ledger. Intents emit them. Projections consume them.

Declaring events

# app.causet
includes:
  events: [./events/**/*.events.causet]

events:
  ARTIST_FOLLOWED:
    state: user
    entity_expr: event.user_id
    payload:
      user_id:   string
      artist_id: string

In this section

Page	What it covers
Concept	Facts vs commands, global event registry
Defining Events	`state`, `entity_expr`, payload types, `kind`
Event Naming	Past tense, domain prefixes
Event Metadata	Envelope fields and `event.ts`
Dispatching Events	`op: emit` from rules
Event Versioning	Safe schema evolution
System Events	Operational event kinds
Testing Events	Fixtures and replay in tests
Best Practices	Reserved fields, naming mistakes
Examples	Concert-domain event catalog

Next steps

Replay — ledger as source of truth
Debugging — Ledger Events — tracing commits
Intents — write path that emits events
Defining Events — start here for DSL syntax

Examples Concept