How do APIs know Bitcoin transaction and wallet types?

Question

I am working on a university project, and I noticed that paid crypto APIs like Whale Alert or Whale Trace return information about transaction types (like exchange), sender and receiver wallets (like private/okex.com/...):

  {
     "hash":"fecb0051e9e69c7e8202fae3866a5193579696c1093049e7e336e5a15d0a9248",
     "from":{
        "address":"bc1qw0c0mrjjw73azm65utnhwvcpsdnpg0cdljg0eg",
        "name":"Wallet",
        "type":"wallet"
     },
     "to":{
        "address":"bc1quq29mutxkgxmjfdr7ayj3zd9ad0ld5mrhh89l2",
        "name":"OKEx",
        "type":"exchange",
        "url":"okex.com"
     },
     "time":"2020-01-24T19:44:03Z",
     "asset":"BTC",
     "size":2763.80593244,
     "USD_size":23417202.542436957
  }

My question is how can I get this information without using these specific APIs? I am new to crypto but I would like to build my own API on the top of Bitcoin (where of course I can't see this information).

Answer 1

I am not sure what API's you are looking for information on. The most common are the bitcoin core API's https://developer.bitcoin.org/reference/rpc/ you have to have a full node running on your machine, but if you just developing you can run core in the testnet or regtest mode so you don't have to download everything

you can download core from here. from there you can decode transaction

bitcoind -testnet -daemon
---wait until that synchs --
bitcoin-cli -testnet gettransaction <transactionid>

you can also use curl to directly access the rpc api if you want other examples. https://bitcoin.org/en/download

Answer 2

You, or someone else working for you, registers to some service, makes transaction/s and see which bitcoins get merged with, or from which address it was withdrawn.

There is probably no easier way how to discover names other than this.

Source: Section "How are names discovered?" at WalletExplorer.com "FAQ: What is on this site?".