A prenuptial agreement can help you and your future spouse in many ways. It offers clear protection for your assets if you should later divorce. You can also put additional things in the agreement, but what goes in must comply with the law.
California Legislative Information explains there are certain things you cannot include or do with your prenuptial agreement. If you include or do things that the law does not allow, it could void that portion of the agreement or lead to a court declaring the whole thing invalid.
Both must sign
The law requires you both to sign the agreement of your own free will. This also requires ensuring each of you understands the details of what you are signing. You both need to have legal representation, a waiver of rights or an explanation of the agreement details when signing.
Terms not acceptable
There are some things you can never include in a prenuptial agreement. One of those is anything pertaining to child custody. Whether you have children now or will have them during the marriage, you cannot dictate custody arrangements or rights within this type of agreement. You also cannot influence child support obligations.
Another thing you cannot do is place limits on the ability of one party to seek remedies for domestic violence. You also cannot include anything that goes against the law or public policy. Including illegal things within the agreement could lead to the whole document being invalid.
The court has the final say as to the validity of a prenuptial agreement. A judge can declare other things within it invalid, but these are the bare minimum of what you cannot do or include.