Variable Substitution

Variables are resolved at request time. Use {{...}} syntax in any request field. This page covers all variable types and where they can be used.

Where Variables Work

Variables are substituted in all of the following fields before a request is sent:

• URL: {{baseUrl}}/users/{{userId}}
• Query parameters: keys and values
• Headers: keys and values
• Body: JSON, text, form data, URL-encoded, GraphQL query and variables
• Authentication: all credential fields (token, username, password, API key, OAuth URLs)

Variable Types

Type	Syntax	Source
Environment / Global / .env	{{name}}	Variables tab and linked file
Dynamic (built-in)	{{$namespace.method}}	Generated at request time
Response chaining	{{$response.body.*}}	Previous response data
Cookie	{{$cookie.name}}	Active cookie jar
Mock data (Faker)	{{$faker.email}}	Realistic fake data via Faker
Prompt	{{$prompt.keyName}}	Prompts for a value at send time
File read	{{$file.read, path}}	Reads file content at send time
Named response	{{RequestName.$response.*}}	Specific request in a runner run

Resolution Priority

When the same variable name exists in multiple sources:

Priority	Source
1 (highest)	Active environment
2	Global variables
3	Linked .env file

Dynamic and response variables always resolve against live data and are not affected by this priority chain.

Dynamic Variables

Dynamic variables generate a fresh value each time a request is sent. They use a $namespace.method format, with optional comma-separated arguments.

UUID

Variable	Description	Example output
{{$uuid.v4}}	Random UUID version 4	550e8400-e29b-41d4-a716-446655440000
{{$uuid.v7}}	Time-ordered UUID version 7	018e7b2c-4a3d-7f6e-8a9b-0c1d2e3f4a5b

Timestamps

Variable	Description	Example output
{{$timestamp.unix}}	Current time as Unix seconds	1706886400
{{$timestamp.millis}}	Current time in milliseconds	1706886400000
{{$timestamp.iso}}	ISO 8601 timestamp	2024-02-02T12:00:00.000Z
{{$timestamp.offset, amount, unit}}	Offset from now (s, m, h, d)	{{$timestamp.offset, 30, m}}
{{$timestamp.format, FORMAT}}	Custom format (see tokens below)	{{$timestamp.format, YYYY-MM-DD}}

Format tokens: YYYY (year), MM (month), DD (day), HH (hour), mm (minute), ss (second).

Random Values

Variable	Description	Example output
{{$random.int}}	Random integer 0–1000	742
{{$random.int, min, max}}	Random integer in range	{{$random.int, 1, 100}} → 57
{{$random.number, min, max}}	Random float in range	{{$random.number, 0.5, 9.5}} → 4.73
{{$random.string}}	16-character alphanumeric string	aB3kR9mPqX2wNv7L
{{$random.string, length}}	String of given length (1–256)	{{$random.string, 32}}
{{$random.bool}}	true or false	true
{{$random.enum, a, b, c}}	Random pick from the list	b
{{$random.name}}	Random full name	Jennifer Garcia
{{$random.email}}	Random email address	jennifer.garcia482@example.com

Hashing

Variable	Description
{{$hash.md5, input}}	MD5 hash (hex)
{{$hash.sha1, input}}	SHA-1 hash (hex)
{{$hash.sha256, input}}	SHA-256 hash (hex)
{{$hash.sha512, input}}	SHA-512 hash (hex)
{{$hmac.sha256, input, key}}	HMAC-SHA256 (hex)
{{$hmac.sha512, input, key}}	HMAC-SHA512 (hex)
{{$hmac.md5, input, key}}	HMAC-MD5 (hex)
{{$hmac.sha1, input, key}}	HMAC-SHA1 (hex)

Encoding and Decoding

Variable	Description
{{$encode.base64, input}}	Base64 encode
{{$encode.base64url, input}}	Base64url encode
{{$encode.url, input}}	URL percent-encode
{{$encode.html, input}}	HTML entity encode
{{$decode.base64, input}}	Base64 decode
{{$decode.url, input}}	URL percent-decode

String Operations

Variable	Description
{{$regex.match, input, pattern, flags}}	First regex match
{{$regex.replace, input, pattern, replacement, flags}}	Regex replace
{{$json.escape, input}}	Escape a string for embedding in JSON
{{$json.minify, input}}	Minify a JSON string

Mock Data (Faker)

Generate realistic fake data. More than 60 functions are available. Type {{$faker. in any field to browse.

Variable	Description	Example output
{{$faker.email}}	Random email address	sarah.j@example.com
{{$faker.fullName}}	Random full name	Sarah Johnson
{{$faker.phone}}	Random phone number	+1-555-0123
{{$faker.uuid}}	Random UUID	550e8400-...
{{$faker.city}}	Random city name	San Francisco
{{$faker.company}}	Random company name	Acme Corp
{{$faker.url}}	Random URL	https://example.com
{{$faker.sentence}}	Random sentence	The quick brown fox...

Prompt at Send Time

Variable	Description
{{$prompt.keyName}}	Shows a dialog prompting for “keyName” before sending. Value is used once and not saved.

File Read

Variable	Description
{{$file.read, /path/to/file}}	Reads the file at send time and substitutes its text content inline.

Response Variables

Reference data from the most recently completed response:

Variable	Description	Example output
{{$response.body.field}}	JSON body field	Value of field
{{$response.body.data[0].id}}	Nested field with array index	42
{{$response.body}}	Entire response body	{"token":"..."}
{{$response.headers.content-type}}	Response header (case-insensitive)	application/json
{{$response.status}}	HTTP status code	200
{{$response.statusText}}	Status text	OK
{{$response.duration}}	Response time in milliseconds	152
{{$response.size}}	Response size in bytes	1024

Named Response Variables (Collection Runner)

In the Collection Runner, reference a specific request’s response by name:

{{Login.$response.body.token}}
{{Login.$response.status}}
{{CreateUser.$response.body.id}}

Names are case-sensitive and must match the request name exactly. If the named request has not run yet, the placeholder is left unresolved.

Cookie Variables

Reference a cookie value by name:

{{$cookie.sessionId}}
{{$cookie.csrfToken}}

The cookie is looked up in the active cookie jar, matched by domain and path against the request URL.

Script-Set Variables

Scripts can write variables using nt.setVar(). Values set in a pre-request script are available for substitution in that same request. Values set in a post-response script are available in all subsequent requests in a collection run.

// Pre-request: set a variable for use in this request
nt.setVar('requestId', nt.uuid());

// Post-response: extract a token for subsequent requests
nt.setVar('authToken', nt.response.json().token);