You're right, this does seem to work [1]. I wasn't aware that serde would attempt to deserialize multiple enum variants until something matches.

[1] - https://serde.rs/enum-representations.html#untagged

Yeah that's a rather common scheme out there so Serde does provide built-in support for this deserialisation. Probably better for deserialisation performances to use properly tagged enums, but if you don't have a choice Serde's got your back.