Great work bitmover, karma earned! You have made so many useful tools but I think Giveaway Manager is your best work.
Can this new service be used to check address balance for some big altcoins, or it only works with bitcoin?
I think that would require running another full node for each coin. Or to have a Blockcypher or Blockchair API key - as free versions will come with daily limits that make balance checkers less useful. Is that correct @bitmover?
There are free api, I use mempool.space for bitcoin. There are certainly free for altcoin, like etherscan
However, there are so many altcoins and layers 2 . For example, there are about 10 (or more?) L2 for ethereum. Base, Linea, zksync, matic, op, Arbitrum...?
There are also ethereum copy cats like bnb...
When I created this project, I thought about focusing in bitcoin only. This was one of the reasons for it.