Certainly before signing the offer letter. I created a website, Friendly Options [1], to act as a helpful ally is trying to extract this information from employers. It asks for a bunch of required information (# of total shares, strike price, share expiration, etc) and then breaks down your option grant in terms and scenarios that are easy to understand. If an employer isn't forthcoming about something you can just say "Look, this website is asking for it and that is why I need it".
Just because a company isn't forthcoming about all the stock option information doesn't mean that startup is unilaterally bad, in some cases the founders are just naive and don't really understand the complexities of your stock options vs their founder stock. However, if you ask the employer for the necessary information to fill out the website and they won't give it to you, then you essentially have no way to value the stock options and the only rational thing to do is value them at $0.
Many people just value stock options at $0 anyways and I don't agree with that. Stock options can be valuable (for example I've made much more money from startup stock options than from salary). However, if you don't have the full information about the stock options you are receiving you can't understand the risk you are taking and the potential rewards you might get.
Just because a company isn't forthcoming about all the stock option information doesn't mean that startup is unilaterally bad, in some cases the founders are just naive and don't really understand the complexities of your stock options vs their founder stock. However, if you ask the employer for the necessary information to fill out the website and they won't give it to you, then you essentially have no way to value the stock options and the only rational thing to do is value them at $0.
Many people just value stock options at $0 anyways and I don't agree with that. Stock options can be valuable (for example I've made much more money from startup stock options than from salary). However, if you don't have the full information about the stock options you are receiving you can't understand the risk you are taking and the potential rewards you might get.
1: http://friendlyoptions.org/