Public knowledge

The number of cards in a player’s hand and Decks, the cards in their Graveyards, and each player’s current Life Points are all public knowledge and both players can verify these things at any time. If asked, you must answer these things to your opponent truthfully.

You are allowed to pick up and verify the cards in your opponent’s Graveyard but you must ask their permission first. Also, you may not change the order of the cards when verifying their Graveyard.