Do full nodes check the validity of all TXs, or just those inside a block?

[Shymaa-Arafat]

I'm sorry if this seems kind of basic or trivial, but do full nodes that are not miners check the validity of each TX; ie, as they appear?
Or just TXs in the blocks they receive, in order to accept or reject the block?

[hosseinimr93]

The (full) nodes verify every transaction they receive.
If your transaction is valid, the (full) node that has received it adds your transaction to its mempool (a database containing unconfirmed transactions) and broadcast it to the other nodes that it is connected to.

[Shymaa-Arafat]

Ok, I get it
That's how transactions propagate
I forgot about it
.
Thanks