helm template --debug or helm install --dry-run --debug , which is best?

The difference between the two commands is that helm install --dry-run will send things to a Kubernetes cluster, but helm template won't.

My general experience has been that debugging intricate Go templates can be tricky, and if I'm having YAML issues (and especially if I have the Kubernetes API documentation up in a browser tab) the helm template output is more than sufficient for my needs, and is a little faster and has fewer dependencies. So I frequently use helm template.

In contrast, by the time I've gotten the Go templating logic and YAML formatting correct, I'm usually ready to actually do a test deployment; so when I helm install it's almost never with --dry-run. If I've gotten the object layout wrong this will still complain, and if it's right then I'm ready to start sending requests to the service.

This is an addition to the answer of David

I always use helm template --debug

A common problem when developing helm templates are whitespace errors (for example incorrect indentations).

Only helm template --debug (but neither helm install nor plain helm template) will generate the invalid yaml, which can be used for easy debugging, because the helm error messages are rarely helpful.