Use helm lint . to verify the syntax of your manifests, given that the current directory contains the Chart.yaml, values.yaml, and template folder containing the manifests.
For example, if I used incorrect indentation:
helm lint .
Error: YAML parse error on app/templates/svc.yaml: error converting YAML to JSON: yaml: line 5: mapping values are not allowed in this context
Use --debug flag to render out invalid YAML