JMeter is a powerful tool for API testing. Let's say you are are writing test cases for one of your RESTful service; and you want to extract and validate the value returned as part of response header. It is little bit tricky to extract the value from Response Header in JMeter , but it is possible. For example, your RESTful service returns "ETag" in response header. When you look at the raw response data, the value is displayed something like this: ETag: 2666d92fa9ebf10250acdb235546f045 To exact value of this reaponse header in JMeter: Right click on your HTTP request, then add Post Processor element - Regular Expression Extractor Select Radio button - Main sample only Select Radio burron - Response Headers Type some name in Reference Name section - for example, eTagVariable Type this expression in Reference Expression section - ETag:\s+(.+) IMPORTANT: This expression will select pick the ETag response header parameter and select everything after colon bla...