Redis WRONGTYPE -- operating on key with wrong type

Redis returns WRONGTYPE Operation against a key holding the wrong kind of value. A GET on a key fails even though the key exists.

Redis keys are typed. A key set with LPUSH is a list, not a string. GET only works on strings. Check key type with TYPE keyname. Common mistake: reusing a key name for a different data structure. Fix: delete the old key first (DEL keyname) or use a different key name. Use consistent naming conventions: user:123:sessions (set), user:123:profile (hash).

Redis stores data in typed structures (string, list, set, hash, sorted set). Operations are type-specific and cannot cross types.