clarkwinkelmann Yes, you could run it like that, but keep in mind that with systems like those simple downtime completely breaks your service, while running it directly in the browser ensures that it is always up when your forum is up and that is doesn't disrupt or gets disrupted by anything in the pipeline when traffic increases.
Also, you don't want to suggest that these performance intensive tools should run on the server, right? Just like spammers abuse the non-existing semantic reasoning, running anything on the server to fix that problem would allow them to simply DDoS your service, if you don't have time delays for posting. Time delays make the experience for normal users worse. Running it locally also allows for real-time analysis which would spread out the overhead over time.
I understand that authenticity of such systems is important here, but there are ways other than running it on the server with which you can ensure that the validation result for a post is authentic.