Dangerous territory here... But I'll bite.
If you can guarantee (likely with a lawyer's advice/help) that you developed it on your own time on your own equipment in your own home, you may have a case to keep it to yourself. Did you sign an Employment Agreement that stated the company owns anything you do? Check that out.
Next, do you have it hosted elsewhere, such as your GitHub page? With a License file attached to it? Added insurance, as most employers will happily take their employee's hard-made products for themselves, because they believe they own the employee. Because they believe this, they want to own anything they create.
Finally, how would your product help the company? Are you willing to do 24/7 support if something breaks, or they want new features added yesterday? You should license it to them, via a company you form, and just happen to be president of. Don't do it as an individual, if you plan on keeping work and private life separate.
Be prepared for them to say no if you charge them, unless it can solve a BIG problem; be prepared to be asked to support it free of charge if they say yes. Good luck