I have been asked many times to review Wills and even Trusts generated online.
Some of them were just fine. This is more often the case with Simple Wills.
Many of the more complex wills and trusts were so defective as to be invalid. They sometimes contained inconsistent or contradictory provisions.
Sometimes they were signed in a way that invalidated them.
Often they had crucial provisions missing.
Another complication is that each state has its own rules. See the quote below from a law professor.
"There isn't a pat answer I can give anyone, that 'here's what it takes to write your own will,'" said Bill McLoughlin, an estate planning attorney and business law professor at Otterbein University in Westerville, Ohio. "Some states recognize oral wills; some don't. In some states, you have to have the will signed at the end and witnessed by two disinterested parties. But some states require three signatures."
Even if no one contests your will, the courts still have to follow the letter of the law. Many courts will not validate provisions if the will is not properly executed (with the proper notarization and number of witnesses). Courts will also balk at provisions that do not make sense. Even uncontested wills can remain in expensive probate limbo, said McLoughlin. https://www.cnbc.com/id/100388275
The short answer to this question is, “Yes, they can be valid, if you follow the rules of your state correctly.”
But the follow up question should be, “Am I willing to risk the future of my family and heirs to an online cost saving substitute?”