ask for license

[srxqds]

Can we use it for free for internal tool development in commercial companies?

[antonfirsov]

2.* yes since it remains under Apache. For vnext (3.0+) the relevant clause of the License is:

Works in Source or Object form are licensed to You under the Apache License, Version 2.0 if.
[...]
You are consuming the Work as a Direct Package Dependency in the capacity of a For-profit company/individual with
less than 1M USD annual gross revenue.
[...]
For all other scenarios, Works in Source or Object form are licensed to You under the Six Labors Commercial License
which may be purchased by visiting https://sixlabors.com/pricing/.

There is no clause distinguishing internal tools from customer-visible products.