Dynamic Variables

Curlex supports dynamic built-in variables that generate fresh, random values at the moment a request is sent. They follow the same {{...}} syntax as regular environment and collection variables, but their names always start with a $ prefix.

{{$guid}}
{{$timestamp}}
{{$randomEmail}}

Dynamic variables can appear anywhere a regular variable can: URL, query parameters, headers, request body, and authentication fields.

Resolution order

When Curlex resolves a {{...}} placeholder it checks in this order:

1. Collection variables — defined on the collection
2. Environment variables — from the active environment
3. Dynamic built-in variables — resolved at send time (this document)
4. Unresolved — the placeholder is left as-is

This means you can override any built-in by defining an environment variable with the same name (including the $ prefix), which is useful for pinning a fixed value in tests.

Every call is independent

If you use the same variable twice in one request, each occurrence produces a separate, independently generated value:

{
  "requestId": "{{$guid}}",
  "correlationId": "{{$guid}}"
}

Both requestId and correlationId will contain different UUIDs.

Variable reference

Identity & UUIDs

Timestamps

Numbers & booleans

Characters & words

Lorem ipsum

Person

Network

Location

Color

Company

Finance

Files & MIME types

Usage examples

Unique user creation

POST /users
{
  "id": "{{$guid}}",
  "name": "{{$randomFullName}}",
  "email": "{{$randomEmail}}",
  "phone": "{{$randomPhoneNumber}}",
  "address": "{{$randomStreetAddress}}, {{$randomCity}}, {{$randomCountryCode}}"
}

Pagination and filtering

GET /products?limit={{$randomInt}}&page=1

Timestamped events

POST /events
{
  "eventId": "{{$guid}}",
  "occurredAt": "{{$isoTimestamp}}",
  "source": "{{$randomUrl}}"
}

Idempotency keys in headers

File upload metadata

{
  "fileId": "{{$guid}}",
  "fileName": "{{$randomFileName}}",
  "mimeType": "{{$randomMimeType}}",
  "uploadedAt": "{{$isoTimestamp}}"
}

Using dynamic variables in test scripts

Dynamic variables are resolved before the request is sent, so their generated values are baked into the actual request. If you need to capture a generated value for assertions in your test script, set it via an environment variable in the pre-request script instead:

// Pre-request script
const id = fc.environment.get('requestId') || crypto.randomUUID();
fc.environment.set('requestId', id);

Then use {{requestId}} in the request body and assert against fc.environment.get('requestId') in the test script.