Nimbostratus
Cirrostratus
You can enter the text of the rule you write in the GUI's rule page and it will verify the syntax before saving the rule.
Else, you can copy the /config/bigip.conf file to a temporary file, edit it to add your rule and then use 'b verify load /config/bigip_test.conf' to verify the syntax of the file.
When you're happy with the changes you can copy the temporary file over the existing bigip.conf file and run 'b load' to initialize the changes. Note that running 'b load' will reset all current connections through the BIG-IP so it should be used to test on a production unit.
Aaron