There's a lot of value in that. Sometimes it's best not to go down the rabbit hole.
Whatever the technicalities might be, the jester definitely followed the normal, reasonable rules of this kind of puzzle, and by those rules he got the right answer. The king set it up that way, and set the jester up to fail.
If he'd done it to teach the jester a valuable lesson about the difference between abstract logic and real life, then it might have been justified. But he's going to have the jester executed, so that argument disappears.
I think we can all agree, The King is definitely a dick.
I'm trying to stay levelheaded about King Richard. What I meant was that there seems to be extraneous details here - about the order things were done in, first inscribe ("key is here", on an empty(?) box), then put dagger in, or that it was written, not spoken. Many comments only enforce the importance of that.
The "real" answer seems to be one that effectively makes all kinds of communication useless, and what I've spent so much time on was trying to pin down the borders of this insanity, some marker saying "abstract logic application to real life* not allowed past this point".
*) the use of physical boxes binding the riddle to "real life"
Once upon a time, there was a court jester who dabbled in logic.
The jester presented the king with two boxes. Upon the first box was inscribed:
On the second box was inscribed:
And the jester said to the king: "One box contains an angry frog, the other box gold; and one, and only one, of the inscriptions is true."
The king opened the wrong box, and was savaged by an angry frog.
"You see," the jester said, "let us hypothesize that the first inscription is the true one. Then suppose the first box contains gold. Then the other box would have an angry frog, while the box with a true inscription would contain gold, which would make the second statement true as well. Now hypothesize that the first inscription is false, and that the first box contains gold. Then the second inscription would be—"
The king ordered the jester thrown in the dungeons.
A day later, the jester was brought before the king in chains, and shown two boxes.
"One box contains a key," said the king, "to unlock your chains; and if you find the key you are free. But the other box contains a dagger for your heart, if you fail."
And the first box was inscribed:
And the second box was inscribed:
The jester reasoned thusly: "Suppose the first inscription is true. Then the second inscription must also be true. Now suppose the first inscription is false. Then again the second inscription must be true. So the second box must contain the key, if the first inscription is true, and also if the first inscription is false. Therefore, the second box must logically contain the key."
The jester opened the second box, and found a dagger.
"How?!" cried the jester in horror, as he was dragged away. "It's logically impossible!"
"It is entirely possible," replied the king. "I merely wrote those inscriptions on two boxes, and then I put the dagger in the second one."
(Adapted from Raymond Smullyan.)