Three different questions
Structural validation asks whether JSON has the expected types, required fields and bounded values. The published JSON Schemas use Draft 2020-12.
Semantic validation asks whether IDs resolve, a reference points to an appropriate object, relevant dependency graphs are acyclic, and time or state relationships make sense. Some of these rules cannot be expressed in JSON Schema alone.
Runtime conformance asks whether a particular implementation actually produces the required appearance, interactions, semantics and motion under declared conditions. That requires rendering and observations.
Passing one layer does not imply passing the next. The repository validator reports structural and implemented semantic checks. The playground's output is an illustrative preview of a subset, not a conformance certificate.
Document conformance
A conforming document declares its version and profiles, satisfies applicable schemas, uses unique addressable IDs, resolves required internal references, and satisfies normative semantic rules. It must not hide required behavior in an unrecognized optional extension.
Implementation conformance
An implementation declares the format version, profiles, modules, extensions and operations it supports. Unsupported required capabilities are errors. An allowed approximation must be reported, including what changed and why. A parser that can retain a field does not thereby implement its rendering behavior.
Visual evidence
A reproducible visual test fixes the target environment: viewport, scale, font availability, locale, color space, animation time, reduced-motion settings and necessary assets. Then it captures evidence and evaluates the selected tolerances.
A pixel comparison can help evaluate a static reference. It cannot prove focus restoration, keyboard navigation, reading order or the meaning of a component. Those require separate observations.
Useful diagnostics
Diagnostics should identify a stable code, severity, document location and a concrete explanation. Runtime reports should include the renderer and version, resolved assets, unsupported capabilities, applied fallbacks and evidence locations. A failed dependency must not be reported as a passing visual assertion.