Built-in Functions

Built-in Functions

Built-in functions are pure, stateless helpers that are evaluated directly inside the workflow expression engine. They require no external credentials and are available in every workflow.

Built-ins are referenced in the workflow AST using their kind discriminant. The tables below list each function, its AST node fields, return type, and a usage example.

Text

LowerCase

Convert a string to lowercase.

Returns: string

{
  "kind": "LowerCaseBuiltIn",
  "value": { "kind": "Literal", "value": "Hello World" }
}

Result: "hello world"

UpperCase

Convert a string to uppercase.

Returns: string

{
  "kind": "UpperCaseBuiltIn",
  "value": { "kind": "Literal", "value": "hello world" }
}

Result: "HELLO WORLD"

Capitalize

Uppercase the first character and lowercase the rest.

Returns: string

{
  "kind": "CapitalizeBuiltIn",
  "value": { "kind": "Literal", "value": "hello world" }
}

Result: "Hello world"

TitleCase

Title-case every word in a string (whitespace preserved).

Returns: string

{
  "kind": "TitleCaseBuiltIn",
  "value": { "kind": "Literal", "value": "hello world" }
}

Result: "Hello World"

TextLength

Count the number of characters in a string.

Returns: number

{
  "kind": "TextLengthBuiltIn",
  "value": { "kind": "Literal", "value": "hello" }
}

Result: 5

StartsWith

Check whether a string begins with a given prefix.

Returns: boolean

{
  "kind": "StartsWithBuiltIn",
  "string": { "kind": "Literal", "value": "https://example.com" },
  "prefix": { "kind": "Literal", "value": "https" }
}

Result: true

EndsWith

Check whether a string ends with a given suffix.

Returns: boolean

{
  "kind": "EndsWithBuiltIn",
  "string": { "kind": "Literal", "value": "report.pdf" },
  "suffix": { "kind": "Literal", "value": ".pdf" }
}

Result: true

TextContains

Check whether a string contains a given substring.

Returns: boolean

{
  "kind": "TextContainsBuiltIn",
  "string": { "kind": "Literal", "value": "Welcome to Lodol" },
  "substring": { "kind": "Literal", "value": "Lodol" }
}

Result: true

Replace

Replace all occurrences of a substring within a string.

Returns: string

{
  "kind": "ReplaceBuiltIn",
  "string": { "kind": "Literal", "value": "foo bar foo" },
  "search": { "kind": "Literal", "value": "foo" },
  "replace": { "kind": "Literal", "value": "baz" }
}

Result: "baz bar baz"

Split

Split a string into an array by a delimiter.

Returns: string[]

{
  "kind": "SplitBuiltIn",
  "string": { "kind": "Literal", "value": "a,b,c" },
  "delimiter": { "kind": "Literal", "value": "," }
}

Result: ["a", "b", "c"]

Truncate

Truncate a string to a maximum length, appending an ellipsis if the string was shortened.

Returns: string

{
  "kind": "TruncateBuiltIn",
  "string": { "kind": "Literal", "value": "Hello, world!" },
  "length": { "kind": "Literal", "value": 5 },
  "ellipsis": { "kind": "Literal", "value": "..." }
}

Result: "Hello..."

IsURL

Return true if the string is a valid http or https URL with no whitespace.

Returns: boolean

{
  "kind": "IsURLBuiltIn",
  "value": { "kind": "Literal", "value": "https://skipflow.com" }
}

Result: true

IsEmail

Return true if the string is a valid email address.

Returns: boolean

{
  "kind": "IsEmailBuiltIn",
  "value": { "kind": "Literal", "value": "user@example.com" }
}

Result: true

Lists

Length

Return the number of items in an array.

Returns: number

{
  "kind": "LengthBuiltIn",
  "value": { "kind": "Literal", "value": [1, 2, 3] }
}

Result: 3

ListContains

Return true if any element in the list is deeply equal to value.

Returns: boolean

{
  "kind": "ListContainsBuiltIn",
  "list": { "kind": "Literal", "value": ["a", "b", "c"] },
  "value": { "kind": "Literal", "value": "b" }
}

Result: true

IndexOf

Return the zero-based index of the first element deeply equal to value, or -1 if not found.

Returns: number

{
  "kind": "IndexOfBuiltIn",
  "list": { "kind": "Literal", "value": ["a", "b", "c"] },
  "value": { "kind": "Literal", "value": "c" }
}

Result: 2

Slice

Return a sub-array from start (inclusive) to end (exclusive). Both indices must be non-negative integers and within bounds.

Returns: array

{
  "kind": "SliceBuiltIn",
  "list": { "kind": "Literal", "value": [10, 20, 30, 40, 50] },
  "start": { "kind": "Literal", "value": 1 },
  "end": { "kind": "Literal", "value": 4 }
}

Result: [20, 30, 40]

Sort

Return a sorted copy of the array. Supports mixed types using Lodol's comparison order: null < boolean < number < string < array < object.

Returns: array

{
  "kind": "SortBuiltIn",
  "value": { "kind": "Literal", "value": [3, 1, 2] }
}

Result: [1, 2, 3]

Reverse

Return a reversed copy of the array.

Returns: array

{
  "kind": "ReverseBuiltIn",
  "value": { "kind": "Literal", "value": [1, 2, 3] }
}

Result: [3, 2, 1]

Append

Return a new array with value appended to the end. The original array is not mutated.

Returns: array

{
  "kind": "AppendBuiltIn",
  "list": { "kind": "Literal", "value": [1, 2] },
  "value": { "kind": "Literal", "value": 3 }
}

Result: [1, 2, 3]

Insert

Return a new array with value inserted at index. The index must be between 0 and length (inclusive).

Returns: array

{
  "kind": "InsertBuiltIn",
  "list": { "kind": "Literal", "value": [1, 3] },
  "index": { "kind": "Literal", "value": 1 },
  "value": { "kind": "Literal", "value": 2 }
}

Result: [1, 2, 3]

RemoveAt

Return a new array with the element at index removed. The index must be within bounds.

Returns: array

{
  "kind": "RemoveAtBuiltIn",
  "list": { "kind": "Literal", "value": ["a", "b", "c"] },
  "index": { "kind": "Literal", "value": 1 }
}

Result: ["a", "c"]

RemoveDuplicates

Return a new array with duplicate values removed (stable order, deep equality).

Returns: array

{
  "kind": "RemoveDuplicatesBuiltIn",
  "value": { "kind": "Literal", "value": [1, 2, 1, 3, 2] }
}

Result: [1, 2, 3]

RandomSample

Return up to count randomly selected unique elements from the list (deep-copied).

Returns: array

{
  "kind": "RandomSampleBuiltIn",
  "list": { "kind": "Literal", "value": ["a", "b", "c", "d"] },
  "count": { "kind": "Literal", "value": 2 }
}

Result: e.g. ["c", "a"] (random)

Math

Round

Round a number to the nearest integer (ties round up).

Returns: number

{
  "kind": "RoundBuiltIn",
  "value": { "kind": "Literal", "value": 2.5 }
}

Result: 3

Floor

Return the greatest integer less than or equal to the value.

Returns: number

{
  "kind": "FloorBuiltIn",
  "value": { "kind": "Literal", "value": 2.9 }
}

Result: 2

Ceiling

Return the smallest integer greater than or equal to the value.

Returns: number

{
  "kind": "CeilingBuiltIn",
  "value": { "kind": "Literal", "value": 2.1 }
}

Result: 3

AbsoluteValue

Return the absolute value of a finite number.

Returns: number

{
  "kind": "AbsoluteValueBuiltIn",
  "value": { "kind": "Literal", "value": -42 }
}

Result: 42

Min

Return the minimum value in a non-empty array of finite numbers.

Returns: number

{
  "kind": "MinBuiltIn",
  "value": { "kind": "Literal", "value": [3, 1, 4, 1, 5] }
}

Result: 1

Max

Return the maximum value in a non-empty array of finite numbers.

Returns: number

{
  "kind": "MaxBuiltIn",
  "value": { "kind": "Literal", "value": [3, 1, 4, 1, 5] }
}

Result: 5

Total

Return the sum of all numbers in an array. Returns 0 for an empty array.

Returns: number

{
  "kind": "TotalBuiltIn",
  "value": { "kind": "Literal", "value": [10, 20, 30] }
}

Result: 60

Mean

Return the arithmetic mean of a non-empty array of finite numbers.

Returns: number

{
  "kind": "MeanBuiltIn",
  "value": { "kind": "Literal", "value": [10, 20, 30] }
}

Result: 20

Mode

Return the most frequently occurring number in a non-empty array. Ties are broken by first appearance; if counts are equal the smaller first-seen index wins.

Returns: number

{
  "kind": "ModeBuiltIn",
  "value": { "kind": "Literal", "value": [1, 2, 2, 3] }
}

Result: 2

RandomInteger

Return a random integer in the inclusive range [min, max].

Returns: number

{
  "kind": "RandomIntegerBuiltIn",
  "min": { "kind": "Literal", "value": 1 },
  "max": { "kind": "Literal", "value": 10 }
}

Result: e.g. 7 (random)

RandomReal

Return a random real number in [min, max). When min == max, returns min.

Returns: number

{
  "kind": "RandomRealBuiltIn",
  "min": { "kind": "Literal", "value": 0 },
  "max": { "kind": "Literal", "value": 1 }
}

Result: e.g. 0.6372 (random)

Date & Time

Now

Return the current UTC datetime as an ISO-8601 string with millisecond precision (e.g. "2025-06-01T12:00:00.000Z").

Returns: string (ISO-8601)

{ "kind": "NowBuiltIn" }

Result: "2025-06-01T12:00:00.000Z" (current UTC time)

Today

Return today's local date as a YYYY-MM-DD string.

Returns: string

{ "kind": "TodayBuiltIn" }

Result: "2025-06-01"

Tomorrow

Return tomorrow's local date as a YYYY-MM-DD string.

Returns: string

{ "kind": "TomorrowBuiltIn" }

Result: "2025-06-02"

Yesterday

Return yesterday's local date as a YYYY-MM-DD string.

Returns: string

{ "kind": "YesterdayBuiltIn" }

Result: "2025-05-31"

UnixTimestamp

Return the current UTC Unix timestamp in whole seconds.

Returns: number

{ "kind": "UnixTimestampBuiltIn" }

Result: 1748779200

WeekdayName

Return the name of the weekday ("Sunday" through "Saturday") for a given ISO-8601 date string, evaluated in UTC.

Returns: string

{
  "kind": "WeekdayNameBuiltIn",
  "date": { "kind": "Literal", "value": "2025-06-02" }
}

Result: "Monday"

TimeUntil

Return the number of whole seconds until the given ISO-8601 datetime (negative if in the past).

Returns: number

{
  "kind": "TimeUntilBuiltIn",
  "date": { "kind": "Literal", "value": "2025-12-31T23:59:59Z" }
}

Result: seconds remaining until that date

Wait

Pause workflow execution for the given number of seconds. Maximum duration is 86400 seconds (24 hours).

Returns: null

{
  "kind": "WaitBuiltIn",
  "seconds": { "kind": "Literal", "value": 30 }
}

IsHoliday

Return true if the given date is a public holiday in the specified region (defaults to "US"). Accepts ISO-8601 date strings or datetime strings.

Returns: boolean

{
  "kind": "IsHolidayBuiltIn",
  "date": { "kind": "Literal", "value": "2025-12-25" },
  "region": { "kind": "Literal", "value": "US" }
}

Result: true

Validation

IsPhoneNumber

Return true if the string is a valid phone number for the given region (defaults to "US"). The region must be an ISO 3166-1 alpha-2 country code.

Returns: boolean

{
  "kind": "IsPhoneNumberBuiltIn",
  "value": { "kind": "Literal", "value": "+14155552671" },
  "region": { "kind": "Literal", "value": "US" }
}

Result: true

Output

Display

Return a deep copy of the given value. Used to surface a value as a visible output in the workflow execution log.

Returns: the same value (deep-copied)

{
  "kind": "DisplayBuiltIn",
  "value": { "kind": "Literal", "value": "Hello, world!" }
}

Result: "Hello, world!"