Lucee 6 adds an optional onMissingKey listener for structs https://luceeserver.atlassian.net/browse/LDEV-3579 for shits n giggles, I hacked it to also fire on accessing struct items https://github.com/zspitzer/Lucee/commit/95df85300cb5bfd443699695680c3cd1da01819d the inspiration which was ironically for Lucee 5 and configImport (which uses a cfml struct internally) was to track which top level keys on the cfconfig.json where ignored / not supported https://github.com/lucee/Lucee/blob/5.3/core/src/main/java/lucee/runtime/tag/CFConfigImport.java#L204