map $request_uri $reject {
    "~[\s]*" 1;
    "~(yandexbot)" 0;
    "~(googlebot)" 0;
    "~(Amazonbot).*" 1;
    "~(SemrushBot).*" 1;
    "~(meta-externalagent).*" 1;
    "~(DataForSeoBot).*" 1;
    "~(Screaming Frog SEO Spider).*" 1;
    "~(GetRight).*" 1;
    "~(GetWeb!).*" 1;
    "~(Go!Zilla).*" 1;
    "~(Download Demon).*" 1;
    "~(Go-Ahead-Got-It).*" 1;
    "~(TurnitinBot).*" 1;
    "~(GrabNet).*" 1;
    "~(dirbuster).*" 1;
    "~(nikto).*" 1;
    "~(SF).*" 1;
    "~(sqlmap).*" 1;
    "~(fimap).*" 1;
    "~(nessus).*" 1;
    "~(whatweb).*" 1;
    "~(Openvas).*" 1;
    "~(jbrofuzz).*" 1;
    "~(libwhisker).*" 1;
    "~(webshag).*" 1;
    "~(Acunetix-Product).*" 1;
    "~(Acunetix).*" 1;
}
#...

server {
    #...
    if ($reject) { return 403; }
    #...
}