Whitelist (coin list)
A fixed set of coins a scanner is allowed to watch — convenient for the vendor, and exactly where the edge is lost.
Most scanners watch a curated list — the top 100 by volume, or whatever the vendor has mapped by hand. It keeps the interface tidy, the backend cheap, and the symbol mapping between exchanges manageable.
It also removes most of the opportunity. Spreads on BTC and ETH between two top venues are arbitraged away in milliseconds by people with colocated infrastructure. The gaps that stay open long enough to trade by hand are on thin coins and fresh listings — precisely what a curated list excludes.
Arbitrex has no whitelist: it indexes whatever each connected venue exposes, and a pair appears as soon as both legs list the same base asset. The cost is that the table is noisier and the burden of checking depth, halts and ticker collisions moves to the trader — which is why depth is rendered next to every row.