System Variables & Functions Reference

The rule engine provides a rich set of system variables (prefixed with @) that give you access to context data, time information, NATS/HTTP metadata, and more.

Message Fields

Variable	Description	Example Value
{fieldName}	Access any field from the message payload	{temperature} → 23.5
{nested.field}	Access nested fields using dot notation	{user.profile.email}
{@msg.field}	Explicitly access root message (important in forEach)	{@msg.batchId}
{@value}	Access primitive value (strings, numbers, booleans at root or in arrays)	{@value} → "ERROR: timeout"
{@items}	Access array at root level	Field reference for root arrays

NATS Subject Context (NATS triggers)

Variable	Description	Example Value
{@subject}	Full NATS subject	sensors.temperature.room1
{@subject.0}	First token of subject	sensors
{@subject.1}	Second token of subject	temperature
{@subject.N}	Nth token (zero-indexed)	room1
{@subject.count}	Number of tokens in subject	3

HTTP Context (HTTP triggers)

Variable	Description	Example Value
{@path}	Full HTTP path	/webhooks/github/pr
{@path.0}	First path segment	webhooks
{@path.1}	Second path segment	github
{@path.N}	Nth path segment (zero-indexed)	pr
{@path.count}	Number of path segments	3
{@method}	HTTP method	POST

Headers (Both NATS and HTTP)

Variable	Description	Example Value
{@header.HeaderName}	Access any header value	{@header.X-Request-ID}
{@header.Content-Type}	Common header access	application/json
{@header.Authorization}	Auth header access	Bearer token123

Time & Date

Variable	Description	Example Value
{@time.hour}	Current hour (0-23)	14
{@time.minute}	Current minute (0-59)	30
{@day.name}	Day of week (lowercase)	monday
{@day.number}	Day of week (1-7, Monday=1)	1
{@date.year}	Current year	2025
{@date.month}	Current month (1-12)	10
{@date.day}	Day of month (1-31)	29
{@date.iso}	ISO date format	2025-10-29
{@timestamp.unix}	Unix timestamp (seconds)	1730217600
{@timestamp.iso}	ISO timestamp	2025-10-29T17:30:00Z

Key-Value Store

Variable	Description	Example
{@kv.bucket.key}	Lookup value from KV store	@kv.users.username
{@kv.bucket.key:field}	Lookup value from KV store with JSON path	@kv.users.{userId}:name
{@kv.bucket.key:nested.field}	Nested field access in KV value	@kv.config.app:db.host

Syntax: {@kv.{bucketName}.{keyName}:jsonPath.nestedValue}

Examples:

# Simple field access
field: "{@kv.device_status.sensor-123}"

# Variable in key name and JSON path
field: "{@kv.users.{user_id}:permissions}"

# Nested JSON path
field: "{@kv.config.app:database.connection.host}"

Cryptographic Signatures

Variable	Description	Example Value
{@signature.valid}	Whether signature verification passed	true / false
{@signature.pubkey}	Signer's public key	UDXU4RCRBVXEZ...

Note: Requires signature verification to be enabled in configuration. See the Security documentation for details.

Template Functions

Function	Description	Example Output
{@timestamp()}	Generate current timestamp (RFC3339)	2025-10-29T17:30:00Z
{@uuid7()}	Generate time-ordered UUID v7	018b7e5a-f3c2-7000-8000-0123456789ab
{@uuid4()}	Generate random UUID v4	550e8400-e29b-41d4-a716-446655440000

Condition Operators

All system variables can be used in conditions with these operators:

Comparison: - eq - Equals - neq - Not equals - gt - Greater than - lt - Less than - gte - Greater than or equal - lte - Less than or equal - exists - Field exists (not null)

String/Array: - contains - String contains substring or array contains element - not_contains - Inverse of contains - in - Value is in array - not_in - Value is not in array

Array Operators: - any - At least one array element matches nested conditions - all - All array elements match nested conditions - none - No array elements match nested conditions

Time-Based: - recent - Timestamp is within time window (e.g., "5s", "1m", "1h")

Complete Example: Using Multiple System Variables

- trigger:
    nats:
      subject: "sensors.*.>"

  conditions:
    operator: and
    items:
      # Time-based: only during business hours
      - field: "{@time.hour}"
        operator: gte
        value: 9
      - field: "{@time.hour}"
        operator: lt
        value: 17

      # Day-based: weekdays only
      - field: "{@day.number}"
        operator: lte
        value: 5

      # KV lookup: check if sensor is active
      - field: "{@kv.sensors.{@subject.1}:active}"
        operator: eq
        value: true

      # Value check
      - field: "{temperature}"
        operator: gt
        value: 25

  action:
    nats:
      subject: "alerts.{@subject.1}.{@date.iso}"
      payload: |
        {
          "sensor": "{@subject.1}",
          "location": "{@subject.2}",
          "temperature": {temperature},
          "sensorName": "{@kv.sensors.{@subject.1}:name}",
          "timestamp": "{@timestamp()}",
          "alertId": "{@uuid7()}",
          "dayOfWeek": "{@day.name}",
          "hour": {@time.hour}
        }