Workflow Studio

Expression Language

Template expressions, JSONata transforms, built-in functions, and the full variable context available inside workflow nodes.

Overview

FlowOS uses a dual expression system: Mustache-style templates ({{...}}) for simple value interpolation in node config strings, and JSONata for complex data transformation in Transform nodes. Both have access to the same runtime context.

Template Syntax

Wrap any JSONata path expression in double curly braces to interpolate its value into a string field:

json

// Simple value
"to": "{{trigger.record.email}}"

// Nested path
"body": "Incident {{trigger.record.number}} assigned to {{trigger.record.assignedTo.name}}"

// Arithmetic
"ttl": "{{nodes.computeTtl.output.hours * 3600}}"

// Conditional (ternary)
"priority": "{{trigger.record.severity = 'P1' ? 'urgent' : 'normal'}}"

// Array index
"firstOwner": "{{trigger.record.cmdbItems[0].ownerEmail}}"

// String concatenation
"subject": "{{'[' & trigger.record.severity & '] ' & trigger.record.title}}"

Runtime Variable Context

The following variables are available in all template expressions and JSONata transforms:

trigger.*

Field	Type	Required	Default	Description
trigger.record	object	optional	—	For record_event triggers: the full record (after change for updates).
trigger.before	object	optional	—	For record_updated: field values before the change.
trigger.changes	object[]	optional	—	For record_updated: [{ field, from, to }] array of changed fields.
trigger.body	object	optional	—	For webhook triggers: parsed request body.
trigger.headers	object	optional	—	For webhook triggers: request headers (lowercased keys).
trigger.event	object	optional	—	For itsm_event and event_bus triggers: the full event payload.
trigger.scheduledAt	timestamp	optional	—	For schedule triggers: intended fire timestamp.
trigger.input	object	optional	—	For manual triggers: the input object passed to the trigger call.

nodes.*

Field	Type	Required	Default	Description
nodes.NODE_ID.output	object	optional	—	The output of a completed node. Only accessible from nodes that run after the referenced node.
nodes.NODE_ID.status	string	optional	—	completed · failed · skipped. Useful in condition expressions.
nodes.NODE_ID.error	object	optional	—	Error details if the node failed: { code, message }.
nodes.NODE_ID.durationMs	integer	optional	—	How long the node took to execute.

vars.*

Field	Type	Required	Default	Description
vars.KEY	any	optional	—	Variables set by set_variable nodes. Mutable across the run.

run.*

Field	Type	Required	Default	Description
run.id	string	optional	—	Current run ID (run_...).
run.workflowId	string	optional	—	Workflow ID that owns this run.
run.startedAt	timestamp	optional	—	When this run started executing.
run.attempt	integer	optional	—	Attempt number (1 = first run, 2+ = retries).

workspace.*

Field	Type	Required	Default	Description
workspace.id	string	optional	—	Workspace ID.
workspace.slug	string	optional	—	Workspace slug.
workspace.name	string	optional	—	Workspace display name.
workspace.config.KEY	any	optional	—	Workspace configuration values set under Settings → Config.

secrets.*

Secrets are write-once, read-in-node. They are resolved at runtime and never appear in logs or traces.

Field	Type	Required	Default	Description
secrets.SECRET_NAME	string	optional	—	Value of a secret stored in the vault. Case-sensitive. Never logged.

JSONata Reference

JSONata is used in Transform nodes and condition expressions. The full JSONata specification is at jsonata.org. Key patterns for FlowOS:

Path navigation

text

trigger.record.title                    // string property
trigger.record.tags[0]                  // first array element
trigger.record.cmdbItems.ownerEmail     // extract field from each array element
trigger.record.cmdbItems[class='server'] // filter array

Constructing objects and arrays

text

// Build a new object
{
  "summary":   trigger.record.title,
  "severity":  trigger.record.severity,
  "owners":    trigger.record.cmdbItems.ownerEmail[],  // force array
  "isP1":      trigger.record.severity = 'P1'
}

// Map array to new shape
trigger.record.cmdbItems.{
  "name":  name,
  "owner": ownerEmail,
  "class": class
}

String functions

text

$string(value)              // cast to string
$uppercase(str)             // "hello" → "HELLO"
$lowercase(str)             // "HELLO" → "hello"
$trim(str)                  // strip whitespace
$contains(str, pattern)     // true/false, pattern can be regex
$replace(str, from, to)     // replace occurrences
$split(str, separator)      // split to array
$join(array, separator)     // join array to string
$length(str)                // string length
$substring(str, start, len) // substring extraction

Numeric functions

text

$sum(array)       // sum numeric array
$min(array)       // minimum value
$max(array)       // maximum value
$average(array)   // arithmetic mean
$round(n, dp)     // round to decimal places
$floor(n)         // round down
$ceil(n)          // round up
$abs(n)           // absolute value
$formatNumber(n, picture)   // e.g. $formatNumber(1234.5, '#,###.00') → "1,234.50"

Array functions

text

$count(array)           // number of elements
$append(a1, a2)         // concatenate arrays
$sort(array, fn)        // sort; optional comparator
$reverse(array)         // reverse order
$distinct(array)        // remove duplicates
$zip(a1, a2)            // merge two arrays by index
$filter(array, fn)      // filter: $filter(items, function($v){ $v.active })
$map(array, fn)         // transform: $map(items, function($v){ $v.name })
$reduce(array, fn, init)// accumulate

Date/time functions

text

$now()                          // current UTC timestamp ISO 8601
$millis()                       // current time in milliseconds
$fromMillis(ms)                 // ms → ISO 8601 string
$toMillis(timestamp)            // ISO 8601 → ms
$dateTime(timestamp, picture)   // format: $dateTime($now(), '[M01]/[D01]/[Y0001]')

Conditional and logic

text

// Ternary
condition ? trueValue : falseValue

// Null coalescing
value ~> $default('fallback')

// Boolean operators
a and b
a or b
not condition

// Comparison
= (equals), != (not equals)
< > <= >=
in (array membership): "P1" in ["P1","P2"]

Real-World Examples

Route based on SLA breach percentage

json

{
  "type": "condition",
  "config": {
    "expression": "(($toMillis($now()) - $toMillis(trigger.record.createdAt)) / (trigger.record.sla.resolutionTarget * 1000)) * 100 >= 75"
  }
}

Build a Slack message with incident details

json

{
  "action": "slack.postMessage",
  "config": {
    "input": {
      "channel": "#incidents",
      "text": "*[{{trigger.record.severity}}] {{trigger.record.title}}*
Assigned: {{trigger.record.assignedTeam}}
SLA due: {{trigger.record.sla.resolutionDue}}
<https://acme.flowos.io/itsm/{{trigger.record.id}}|View Incident>"
    }
  }
}

Filter and reshape CMDB items for downstream use

json

{
  "type": "transform",
  "config": {
    "expression": "trigger.record.cmdbItems[class='server'].{ 'host': hostname, 'ip': ipAddresses[0], 'owner': ownerEmail }",
    "outputAs": "affectedServers"
  }
}
// Access as: {{nodes.TRANSFORM_NODE_ID.output.affectedServers}}