Whistl Developer Guide & API Credentials

Overview

This developer guide shows how to access Whistl shipping API via AfterShip Shipping, and Whistl web service. See also the list of required API credentials / keys for Whistl integration.

Get Whistl Developer Credentials

Email Whistl sales representative and cc [email protected] Tell Whistl you need to obtain Whistl web service API credentials.
Whistl will provide testing credentials for Sandbox environment: Client Code, Site Code and Customer Number
Use the Whistl testing credential to generate a label via AfterShip Shipping Sandbox environment. Send Whistl the sample label, together with request and response xml files.
Whistl will provide the production credentials for Whistl web services API: Client Code, Site Code and Customer Number

Required Whistl API credentials

Credentials	Environment	Description
customer_number	Sandbox / Production	Your Whistl customer account number.
client_code	Sandbox / Production	Testing API credentials to access Whistl web service and Postmen API.
site_code	Sandbox / Production	Testing API credentials to access Whistl web service and Postmen API.

Whistl Developer Resources

Read Whistl docs
Supported Whistl service types and service options
AfterShip Shipping Whistl technical support: [email protected]

Updated on: 27/10/2025