Writing pre-request scripts

You can use pre-request scripts in Postman to execute JavaScript before a request runs. By including code in the Pre-request Script tab for a request, collection, or folder, you can carry out pre-processing such as setting variable values, parameters, headers, and body data. You can also use pre-request scripts for debugging code, for example by logging output to the console.

An example usage of pre-request scripting could be as follows:

  • You have a series of requests in a collection and are running them in a sequence, e.g. using the collection runner.
  • The second request is dependent on a value returned from the first request.
  • The value needs to be processed before you pass it to the second request.
  • The first request sets the data value from a response field to a variable in its Tests script.
  • The second request retrieves the value and processes it in its Pre-request Script, then sets the processed value to a variable (which is referenced in the second request, e.g. in its parameters).

Scripting before your request runs

To include code you want to execute before Postman sends a request, open the request and select the Pre-request Script tab.

Pre Request Tab

Enter the JavaScript you need to process before the request runs.

Pre Request Code

When you click Send, the code will execute before Postman sends the request to the API.

Re-using pre-request scripts

You can add pre-request scripts to entire collections as well as to folders within collections. In both cases, your pre-request script will run before every request in the collection or folder. This allows you to define commonly used pre-processing or debugging steps you need to execute for multiple requests.

To add pre-processing to a group of requests, locate the collection or folder in Collections on the left of Postman. Click ... to View more actions and select Edit.

Collection Actions

Open Pre-request Scripts to enter code that will run before every request in the collection or folder.

Collection Pre Request Script

You can define a pre-request script when you first create a collection or folder, or at any time after that.

Next steps

For more detail on what you can do in your pre-request scripts, check out Test Scripts and the Postman Sandbox.