Template helpers

This is the reference list. For the concept and a worked example, start with templating.

Activation

Scope	How
One stub	"transformers": ["response-template"] on the response
Whole host	Start the server with --global-response-templating
Webhooks	Automatic — webhook fields are templated with no transformer needed

Note

Helper arguments use single quotes: {{jsonPath request.body '$.user.id'}}. Double quotes inside a JSON stub would terminate the surrounding string.

The request model

These are data paths, not helpers — read them directly.

Path	Value
request.method	HTTP method
request.url	Full URL including query string
request.path	Path; request.path.[n] for a segment; request.path.<name> when the stub used urlPathTemplate
request.pathSegments.[n]	Path segment by index
request.query.<name>	Query parameter
request.headers.<Name>	Request header
request.cookies.<name>	Cookie
request.body	Raw body
request.bodyAsBase64	Body, base64-encoded
request.host
request.port
request.scheme
request.baseUrl
request.parts.<name>	Multipart part; has .body, .name, .headers.<H>

Named path variables such as request.path.id only resolve if the stub matched through urlPathTemplate. See request matching.

The root object differs by context:

Context	Root
Response templating	request
Webhook	originalRequest
WebSocket message mapping	message.body

Data helpers

Helper	Purpose
jsonPath	Extract a value from JSON with a JSONPath expression
xPath	Extract a value from XML with an XPath expression
regexExtract	Extract a capture from a string with a regex
formData	Read a form-encoded body into named fields
parseJson	Parse a JSON string; available in inline and block form
assign	Bind a value to a name; block form

Date helpers

Helper	Purpose
parseDate	Parse a string into an instant
date	Format an instant
now	Current time; accepts offset= and a format pattern
truncateDate	Truncate an instant to a unit

Note

On date, a timezone= argument is deliberately ignored when the input is an already-parsed instant. This matches WireMock, so the two produce identical output; it is not an oversight.

Random helpers

Helper	Purpose
randomValue	Random value of a given type=, e.g. UUID
pickRandom	Pick one element at random
randomInt	Random integer
randomDecimal	Random decimal

JSON helpers

Helper	Purpose
jsonArrayAdd	Append to a JSON array
jsonMerge	Merge two JSON objects
jsonRemove	Remove a node from JSON
toJson	Serialize a value to JSON

Format, math, string and array helpers

Helper	Purpose
math	Arithmetic; supports + - * / only
numberFormat	Format a number
size	Length of a string or collection
join	Join a collection with a separator
substring	Substring by index
replace	Replace occurrences in a string
upper	Uppercase
lower	Lowercase
capitalize	Capitalize
trim	Strip surrounding whitespace
base64	Base64-encode
urlEncode	URL-encode
formatJson	Pretty-print JSON
formatXml	Pretty-print XML
isOdd	Odd-number test
isEven	Even-number test
range	Produce a numeric range
array	Build an array from arguments
lookup	Read a value out of a collection by key or index
arrayAdd	Append to an array

System helpers

Helper	Purpose
systemValue	Read a system/environment value
hostname	Host name of the running server

Caution

systemValue is deny-by-default. Every key renders [ERROR: Access to <key> is denied], and there is no allowlist mechanism to open specific keys. Do not build stubs that depend on it. For values you control, use environments instead.

Fake data

One helper, random, taking a Datafaker-style expression string:

{{random 'Name.fullName'}}

Class	Methods
Name	firstName, lastName, fullName, name, username, prefix
Internet	emailAddress, url, uuid, domainName, ipV4Address, macAddress
Address	city, country, countryCode, zipCode, state, stateAbbr, streetAddress, streetName, buildingNumber, secondaryAddress, fullAddress, latitude, longitude
Number	digit
Company	name
Commerce	productName
Lorem	word, sentence
PhoneNumber	phoneNumber, cellPhone

An unrecognised expression renders the literal text [ERROR: Unable to evaluate the expression <expr>] into the response rather than failing the request.

Argument-taking faker expressions such as Number.numberBetween are not supported. Locale selection is not supported either.

Note

{{random 'Internet.url'}} returns a scheme-less host such as www.foo.co, matching Datafaker. This changed in v0.8.0 — stubs written against an earlier version that expected a leading https:// need updating.

JWT helpers

Helper	Purpose
jwt	Produce a signed JWT
jwks	Produce a JWKS document

Caution

jwt supports HS256 and RS256. A configurable signing secret, the nbf claim, and array or object claim values are not supported.

Handlebars built-ins

{{#if}}, {{#each}}, {{#unless}} and {{#with}} are available as normal.

Helpers that do not exist

Several helper names appear in third-party references and even in the dashboard’s helper popup, but are not registered in the engine. The engine is the authority.

Name	Use instead
add	math
subtract	math
multiply	math
divide	math
round	—
abs	—
soapXPath	xPath

Caution

All arithmetic goes through the single math helper, which supports + - * / and nothing else. There is no rounding or absolute-value helper.

Note

The in-app dashboard’s helper popup currently lists some of these names in error. If the popup and this page disagree, this page is correct.