Why do you have to search for TXIDs in little-endian? I understand that when you double-sha256 some transaction data, it will give you the TXID for that transaction. This can then be used in future transaction data when you want to reference an existing transaction.

However, if you want to search for a TXID using bitcoin-cli or a blockexplorer, you have to convert this TXID to little-endian.

TXID (original):  B0570984EA35E417A20327D72414CDA0EB8200418772FA3E1A28D76EF4977CF2
TXID (searching): F27C97F46ED7281A3EFA7287410082EBA0CD1424D72703A217E435EA840957B0


What's the reason for this?
Because Bitcoin in general uses little-endian while most hashing libraries use big-endian.

For more details and links see here.