Is the conversion lossless?
No, and no YAML-to-JSON conversion is. Comments, anchors, merge keys, tags and block style have no JSON equivalent, so they are resolved or dropped. What is different here is that each one is counted and located instead of disappearing quietly.
Will the result turn back into the same file?
JSON does: converting JSON to YAML and straight back produced byte-for-byte identical JSON on all three real files we tested, number literals and key order included. YAML does not: comments are gone, anchors and merge keys are expanded, and quoting changes. The values survive the round trip; the file as you wrote it does not.
Why did my yes turn into a string?
Because this tool reads YAML 1.2, where yes is text. PyYAML, Ruby and Go's yaml.v2 read YAML 1.1, where the same word is true. Those are exactly the lines the mismatch list flags, so you see them here rather than in a broken deploy.
Does it round my numbers?
No. The JSON is written from your source text rather than from a JavaScript number, so 9007199254740993 and 1.10 are printed exactly as you typed them. Key order survives too, including numeric-looking keys such as 10, 2 and 1, which a plain JavaScript object would silently reorder to 1, 2, 10.
Can it open CloudFormation or Ansible files?
It opens them without failing, !Ref and !GetAtt are accepted and their values kept: but the tag itself is dropped, so what you get back is data, not a template you can deploy.
Is my file uploaded?
No. The conversion runs in your browser tab. That matters more here than on most pages: Kubernetes manifests and CI workflows routinely carry internal hostnames, registry addresses, secret names and sometimes the secrets themselves.