How Does a Transaction Become Visible in the Mempool?

A transaction becomes visible in the mempool immediately after a user signs and broadcasts it to the network. The user's wallet or node sends the signed transaction to one or more full nodes, which validate its basic structure and then relay it to other nodes in the network.

This broadcasting process is what places the transaction into the memory pool of all listening nodes, making it publicly available for block producers and front-running bots to see.