The decoder keeps a search log so that missing coverage can be found: the maker, the code system, whether the lookup matched, and the method that answered. The log is written with a keyed hash of the IP address and the user agent rather than the values themselves, and it is kept for ninety days.
There are no accounts on this site, no user profiles and no selling of data. The log is used to see which codes are asked about and which tables are missing entries.
Traffic measurement uses Google Analytics with the anonymised settings used across this group of reference sites, plus the Bing and search-engine verification meta tags required for indexing. Those services receive the page address and standard request data under their own policies.
Outbound links to marketplaces and shops may carry an affiliate tag, which is how the reference is funded. That tag tells the destination that a visitor arrived from this site; it does not pass on any code you typed into the decoder.
Nothing you enter in the decoder is shown to third parties or used to identify you, and no contact details are collected unless you send them to the address on the contact page yourself.