A HTTP Archive (HAR) is nothing else but a plain text file. The data in it is stored as JSON, so you can open the file with any text editor or JSON editor. You could simply try renaming the .har extension to .json.
The HAR file will primarily list all of the network requests and responses the browser makes and receives. This includes basically everything you see in the Network tab from Google Chrome, like the specific URL of a request, but also all of the HTTP GET and POST parameters. Of course, the HAR file also contains timings, so you can see how long it took to load some resource.
"request": {
"method": "GET",
"url": "http://www.example.com/path/?param=value",
"httpVersion": "HTTP/1.1",
"cookies": [],
"headers": [],
"queryString" : [],
"postData" : {},
"headersSize" : 150,
"bodySize" : 0,
"comment" : ""
}
Here you can see that example.com/path was requested and the param GET parameter was sent, with its value set to value.
Of course, this data alone will not enable you to track down an error, especially not if you're just the user of a website, without access to the actual backend. The developers however can "replay" a HAR file, meaning that they can try doing what you did and see whether they can reproduce the errors, especially since they also have the cookies. This makes it possible to pretend that they're you when using the website.
Mind you that since all the data sent to the server is saved in the HAR file, any login data or private information you sent through a form will also be saved. That means, for example, when you log into a website, and create a HAR from these requests, your password is saved in plain text.
So make sure to check the contents of the file and don't submit anything you wouldn't want the developers to see.
