The following query parameters are use by Solr for all requests...
Parameters That Affect Processing
qt
If a request uses the /select URL, and no SolrRequestHandler has been configured with /select as its name, then Solr uses the qt (query type) parameter to determine which Query Handler should be used to process the request. Valid values are any of the names specified by <requestHandler ... /> declarations in solrconfig.xml
The default value is "standard".
wt
The wt (writer type) parameter is used by Solr to determine which QueryResponseWriter should be used to process the request. Valid values are any of the names specified by <queryResponseWriter... /> declarations in solrconfig.xml
The default value is "standard".
Parameters That Produce Debugging Info
echoHandler
If the echoHandler parameter is true, Solr places the name of the handle used in the response to the client for debugging purposes.
echoParams
The echoParams parameter tells Solr what kinds of Request parameters should be included in the response for debugging purposes, legal values include:
none - don't include any request parameters for debugging
explicit - include the parameters explicitly specified by the client in the request
all - include all parameters involved in this request, either specified explicitly by the client, or implicit because of the request handler configuration.