How can I constrain the docker usage to a spesific number of cores

I have multiple dockers with different services running on the same server with Intel Xeon-E 2386G - 6c/12t.

One of the dockers runs heavy service on it, I want to make sure it never uses more than half of my CPU power and RAM.

After looking it up, it appears that Intel Xeon-E 2386G - 6c/12t has 6 cores and 12 threads.

From the docker documentation it isn't clear to me how to define this limit, this is what I come up with:

deploy:
  resources:
    limits:
      cpus: '3'

Is this really do what I think it does? do this limit the service usage to a maximum of half of my CPU power?