Understanding blockchain RPCs from scratch

A few days ago I deployed gasfee.oeduardoal.dev , a small tool that shows real-time transaction fees across 7 different blockchains. The UI is simple, but building it forced me to understand something I had always glossed over: how does your code actually talk to a blockchain? If you are a backend dev who has never touched Web3, this one is for you. What is a blockchain, from a backend perspective? Think of a blockchain as a database you do not own. It is a distributed ledger running across thousands of nodes worldwide. There is no single server. It is a network of computers that all agree on the same state. As a backend dev, your instinct is: "okay, so how do I query it?" That is where RPCs come in. What is an RPC? RPC stands for Remote Procedure Call. In the blockchain world, it is the interface between your app and a node on the network. You do not run the node, you just call it. It works over HTTP and looks like this: POST https://eth.llamarpc.com Content-Type: application/json { "