I am not honestly familiar with Timoni, but glancing through the docs it looks like it heavily centered around Kubernetes deployments? Our initial use cases were centered around IaC for non-k8s workloads (think systems such as ECS or Cloud Run).

In terms of the YAML aspect, internally the core system does not use YAML. We opted to stick with YAML as the interface for the time being purely because it is familiar and there's loads of tooling.

We've been working to improve the structural and the type checking further and I'm hopeful to have a substantial improvement to that released "soon." It is queued up behind some other improvements within the language server we need to make first though.

It's YAML.