ApacheBench
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ApacheBench is a command line computer program to measure the performance of the Apache web server. It is designed to give an idea of the performance that a given Apache installation can provide. In particular, it shows how many requests per second the Apache server installation is capable of serving. The ab tool comes bundled with the Apache source distribution, and like the Apache web server itself, it is free, open source software and distributed under the terms of the Apache License.
The ApacheBench User Agent string is the following:
ApacheBench/1.3d