What is an API (Application Programming Interface) 

API is consists of a specific set of rules/guidelines/logic of the application.

  • It helps us to interact with two Softwares/Apps.
  • We will use API’s to simplify the complexity.

Example: Searching for an Email based on sent To address.

API Code snippet for search email:
Mailosaur client = new MailosaurClient(“YOUR_API_KEY”);
SearchCriteria criteria = new SearchCriteria();
List<MessageSummary> results = client.messages().search(“SERVER_ID”, criteria);
MessageSummary latestEmail = results.get(0);

Here we are using existing Mail API to establish connection and to check email messages. The current Mailosaur API is a generic API for all.


API needs HTTP for transport data over the internet.

  • HTTP(Hypertext Transport Protocol) is an application layer protocol that is used to transmit the data between two different systems/hosts over the network.
  • HTTP is a stateless protocol – Doesn’t care about an earlier request
    Web API is required the internet to interact with applications.
  • All API’s are not required to be web API’s as we also have native API’s like webdriver API(selenium).

How HTTP Request and Response works

  • HTTP communication should happen through TCP (Transmission Control Protocol) /ip connection. It means client and server should have a qualified IP address (32 bit) and Port(HTTP:80 and HTTPS:443)

 HTTP Request and Response Process

  • HTTP will initiate a connection between the source and destination systems.
  • Client Send a request to the server through HTTP protocol
  • Server processed the request and send back a response

HTTP Methods

HTTP Get Request

HTTP Get Response 

HTTP Response Codes

Reference: https://en.wikipedia.org/wiki/List_of_HTTP_status_codes

Sample Request methods

  • GET : Accessing facebook Login Page
  • POST: https://www.facebook.com/ register
  • DELETE: Deleting file from trash


  • HTTP is not secured when we want to use sensitive data on internet.
  • HTTPS is more secure to use as its encrypt the data during transit phase.
  • We use SSL(Secure Sockets Layer)/TSL(Transport Layer Security) digital certificates at webserver to make use of HTTPS protocol.


  • SOAP (Simple Object Access Protocol) is a protocol.
  • REST (Representational State Transfer) is an architectural style.
  • REST can also use SOAP protocol to develop a specific functionality.
  • SOAP API uses WSDL (Web Services Description language) for describing the functionalities.
  • Enterprise applications uses WADL (Web Application Description Language) to define rest apis functionality.
  • The Web Application Description Language (WADL) is a machine-readable XML description of HTTP-based web services.

SOAP Request and Response Format

REST Example


Most popular tools for API Automation

  • REST-Assured: It is really good when you have good number of regression test cases which is fall under behaviorial driven scenarios.
  • Postman : It is mostly used when you want to automate smoke tests.
  • SOAP UI: It is useful when we have complicated functional scenarios. 


    Happy Learning 🙂