If it is strictly free online tool you want, then you might be out of luck. None of the services that perform cross browser and multiple devices (Mobile, TV, Tablets and Desktop) testing are free. (Many have either 14 day or 30 days trial)
But if you are willing to pay a little, I'd recommend you to try Browser Stack.
A 30 ...
I recommend Cypress, which we use on a big project. Cypress builds on top of Mocha and adds a enough of convenience to allow all our QA engineers to write tests with little training needed.
(Though we're adding one more layer of abstraction on top, because our bottleneck is the translation between test scenario documents and test code. Our project's ...
Maybe try one of the following:
In Chrome, open DevTools and click on Toggle device toolbar, then in the dropdown menu:
Edit -> Add custom device...