Various examples are directed to methods and systems for describing message payload data in computer messaging. A messaging client may receive a first message that comprises first payload data. The messaging client may identify from the first message a first metadata identifier data and send a metadata request to a metadata source indicated by the first metadata identifier data. The messaging client may receive from the metadata source first payload metadata describing the first payload data. The messaging client may identify a first payload record from the first payload data based at least in party on the first payload metadata.