This assumes you wrote the project without company tools and on your free time.

Even then. some employment contracts try to take the piss and claim ownership of anything you produce while you’re employed. Clauses like that are unenforceable in many jurisdictions, but I’ve taken the liberty of redlining them before signing the contract. That means another half-day wating for Legal to look at it, but it’s worth it for the removal of ambiguity about what I intend to do. By the way, I’ve never had an offer withdrawn for doing that.