What is a HAR File and what is the use of HAR?

HAR stands for HTTP Archive. 

This is a common format for recording HTTP tracing information. This file contains a variety of information, but for our purposes, it has a record of each object being loaded by a browser. Each of these objects’ timings is recorded.

The HAR file format is still an evolving standard, and the information contained within is both flexible and extensible. You should expect the HAR file to include a breakdown of timings including:

• how long it takes to fetch the DNS information
• how long each object takes to be requested
• how long it takes to connect to the server
• how long it takes to transfer from the server to the browser of each object
• whether the object is blocked or not

The data is stored as a JSON document and extracting meaning from the low level data is not always easy, but with practice, a HAR file can quickly help you identify the key performance problems with a web page, which in turn will help you efficiently target your development towards the areas that will deliver the greatest return on your efforts.