WRONGTYPE: WRONGTYPE Operation against a key holding the wrong kind of value

What does it mean?

A command was run against a key that is not appropriate for that key's data type. For example, applying a list (LPUSH) or hash (HSET) command to a key holding a string.

Why does it happen?

The key is of a different type than expected, the same key name is used with different data types, type confusion in the application logic, or an old/leftover key being overwritten.

How to fix it

Check the key type: TYPE mykey. Choose the command according to the key's actual type. Distinguish types in key naming (e.g. a set for user:1:tags, a string for user:1:name). If needed, delete the old key (DEL) and recreate it with the correct type. Enforce type consistency in the application layer.