"What are the tools B2B founders can use to get to message-market fit?"
Message-market fit is difficult to find, because it consists of multiple disciplines. There a few different tools that we normally recommend, bearing in mind that this all needs to take place at the intersection between human relations, connection and communication.
Firstly, you have to know the literature relating to message-market fit inside out. A good example is "Zero to One" by Peter Thiel, which discusses the importance of niches.
Another great read is "The Lean Startup" by Eric Ries, which talks about selling before building. Get to grips with this material, especially the fact that your product doesn't have to be ready to make a compelling offer and find the right message-market fit.
"The Mom Test" by Rob Fitzpatrick is also a must-read, which provides you with the questions to ask potential customers about your business.
What tools will this literature help you build?
Anything you would normally do in the sales process can lead you to message-market fit, but it entails perseverance.