The filter I'm gathering data on is called minRelayTxFee -- minimum relay transaction fee. Almost every bitcoin transaction pays fees to miners, and most nodes have a standard filter that checks every transaction sent to its mempool to see if it pays a minimum fee. If not, it refuses to relay that transaction. Thanks to most nodes doing this, there is a mitigation for what would otherwise be a significant DoS vector on bitcoin: without this filter, spammers could cheaply DoS the network by sending out millions of 0-fee transactions. In the op_return wars, people who oppose spam filters have been arguing for a while now that spam filters "don't work" because some large op_returns bypass the spam filters and get into the blockchain via private mempools, or libre-relay. One of the pro-filter side's responses is that these are exceptional cases; only a small percentage of transactions in the blockchain show any evidence of bypassing the op_return filters, and that helps prove that the filters work. Recently, the anti-filter crowd has a new argument: spam filters "don't work" because some transactions pay less than the standard minimum feerate; they bypass the minRelayTxFee filter. So I created this website to gather statistics about that, and show that the same counterargument applies: only a small percentage of transactions in the blockchain show any evidence of bypassing the minRelayTxFee filter, and that helps prove that the filters work.

The reason the minRelayFee filter works is because there is very little economic incentive to bypass it. It is cheaper to just bump your fee to 1 sat/vbyte. This is not so for larger OP_RETURN txs or other types of non-standard txs.