The mempool has no proof-of-work — it can't be verified, only witnessed. So this page compares independent public witnesses, re-verifies every transaction it inspects by hashing the raw bytes, and — the part only consensus can settle — measures each mined block against the mempool view that preceded it: transactions that were never seen publicly before being mined, per pool. A WS-to-TCP bridge to a real node (your own independent witness) is the roadmap.
Method: a full txid snapshot of the public mempool is taken every 2 minutes (plus the live sample stream); when a block is mined, its txids (from the consensus block, coinbase excluded) are checked against everything seen before it. "Dark" is an upper bound — a tx arriving in the final seconds before its block counts as unseen. Blocks arriving with a stale snapshot are recorded without a dark measurement.