[borski]

Depends. If you are a contractor, like most craftspeople, your tools are your own.

[ninjalanternshk]

My contracts always state I own tools created or byproducts of the work that don't end up in the work.

[pjmlp]

Only if you are self employed, otherwise it belongs to the agency.

[borski]

Again: it depends. It is all about how the contract is written.

[pjmlp]

I never seen any other kind of contract, on my 50ys.

[borski]

You're definitely right for most agencies; most will let you use it in a portfolio or something, but not necessarily retain the rights to the work.

Some agencies do, however; it's dependent on the contract specifics.

[krzyk]

I'm curious how does it work, you handover the tools you wrote, .bashrc/.zshrc, etc?

When I'm hired in a company (not contract), they wipe the harddrive when I leave (well, I also do it before I hand it over sometimes). So they don't get the tools (I take them with myself, it would be a waste to loose them)

[borski]

If you are a W2 employee in the US, you are almost certainly in violation of your PIIA if you take anything off the company-issued computer and keep it.

[pjmlp]

How do you take them with you in first place, without doing data thef?

As per NDAs and work contracts, nothing is supposed to leave either employer nor customer systems into unauthorised third parties.