XSS without Browser

To all Sec guys, I had been cracking my brain over these past 2 weeks thinking on how do i verify successful XSS attacks without using the browser. I know it sound absurd, but that's the way it is. All i have is pcap files available. From those pcap files, we can obviously search for those "script" word or other variants of XSS attacks by using regular expression. However, how do we know if an attempt is successfully executed or just false positive. Looking at the HTTP 200 response code, that will tell me that the attempt went through, but how do we know if we are truly exploited. Javascript maybe?

The Hacka Man