Specifiy index, host, source, soucetype for the events, This can be used in Splunk query language such as index="main" source="jenkins" host="jenkins.domain" sourcetype="_json"

The index in Splunk to which the events will be indexed to. Defaults to "main" index in Splunk. Note: If using a custom index, that index must be already exist on your Splunk instance. Splunk-Jenkins will not create it for you.

The metadata can be customized for each event prefix: test_result, console_log, queue_info, file, xml_config e.g.

    #index
    index=main #this is global level
    console_log.index=ci_log #only for console_log
    #source
    source=sandbox
    #sourcetype
    sourcetype=_json
    #host
    host=sandbox
    
will set index as ci_log for console_log event, main as index for others. jenkins_job as source for console_log event, sandbox as source for others
Note: double quote is not needed for values.