jack of all trades, master of none
Definition from Wiktionary, the free dictionary
See also jack of all trades
This phrase has itself been (rarely) expanded to a couplet:
- Jack of all trades, master of none,
- though oftentimes better than master of one.
- (idiomatic) A person who has a competent grasp of many skills but who is not outstanding in any one.
person who has a competent grasp of many skills