I usually take a subscription to Expertflyer for a month or two while I'm setting up an RTW, and use it to check for D class (or whatever you are flying in) on specific flights before asking the tool to price the route and again before calling to book.
I agree with @SPO, except that I have an annual subscription to Expert Flyer, as I use it all the time. I would not rely on the online tool to verify if a routing is correct, as it is often wrong. I verify the routing against the rules myself, manually, then use Expert Flyer to identify the flights I want and verify availability in the appropriate booking inventory.