Rules

A rule looks inside an event and decides, before any delivery is created, whether to add an endpoint, change the payload, or stop the event.

How a rule runs

1. Your system sends an event, and Railhook stores it.

2. Enabled rules whose eventTypePattern matches the event type are collected, highest priority first.

3. Each rule’s condition tree is evaluated against the payload. A rule with no conditions matches every event of its type.

4. The actions of every matching rule are applied, then subscriptions are matched and deliveries are created.

Order matters

Rules run before subscriptions are matched. A DROP therefore stops the event before a single delivery exists: the event is still stored and the API still answers 201, but nothing is sent. Give a rule without conditions a narrow event type pattern.

Actions

Action	What it does
ROUTE	Delivers the event to endpointId, whether or not a subscription points at that endpoint. An endpoint already reached through a subscription does not get a second delivery.
TRANSFORM	Applies the saved transformation transformationId instead of the subscription’s own. When several matching rules transform, the last one wins.
DROP	Stops the event. The first matching rule with DROP ends evaluation, and no delivery is created.
TAG	Accepted with a config object. It does not change which deliveries are created or what they carry.

A rule can carry several actions; sortOrder sets their order.

Conditions

Conditions form a tree of groups and predicates.

Node	Fields
Group, "type": "group"	op: AND, OR or NOT; children: groups or predicates.
Predicate, "type": "predicate"	field: a dot-separated path in the event’s data, such as customer.email or items[0].sku; operator; value; valueType; optional caseInsensitive.

Operators
Comparison	EQ, NEQ, GT, GTE, LT, LTE, BETWEEN
Text	CONTAINS, NOT_CONTAINS, STARTS_WITH, ENDS_WITH, REGEX
Sets	IN, NOT_IN
Presence	EXISTS, NOT_EXISTS, IS_NULL, NOT_NULL

valueType is one of STRING, NUMBER, BOOLEAN, ARRAY_STRING, ARRAY_NUMBER, DATE_TIME.

Example: route high-value orders

Any order.* event with an amount of 1000 or more, in USD or EUR, also goes to a fraud-check endpoint, on top of whatever its subscriptions already do.

curl -X POST "$RAILHOOK_URL/api/v1/projects/$PROJECT_ID/rules" \
  -H "X-API-Key: $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Route high-value orders to fraud detection",
    "enabled": true,
    "priority": 10,
    "eventTypePattern": "order.*",
    "conditions": {
      "type": "group",
      "op": "AND",
      "children": [
        { "type": "predicate", "field": "amount", "operator": "GTE", "value": 1000, "valueType": "NUMBER" },
        { "type": "predicate", "field": "currency", "operator": "IN", "value": ["USD","EUR"], "valueType": "ARRAY_STRING" }
      ]
    },
    "actions": [
      { "type": "ROUTE", "endpointId": "'"$FRAUD_ENDPOINT_ID"'", "sortOrder": 0 }
    ]
  }'

Turn a rule on or off with PATCH /api/v1/projects/{projectId}/rules/{id}/toggle.

Next steps

TransformationsWrite the transformation a TRANSFORM action applies.

Endpoints and subscriptionsThe matching that runs after rules.

WorkflowsMulti-step logic that runs when an event arrives.