Text and markup

These are plain text that people read and edit as often as programs do. JSON is the data format of web APIs, defined by one small grammar. XML marks up trees of tagged text and still defines Office documents, SVG and RSS feeds. YAML and TOML are mostly used for configuration, from Kubernetes manifests in YAML to Cargo.toml and pyproject.toml in TOML.

They differ most in how they handle types. JSON has strings, numbers, booleans, null, arrays and objects, and nothing else, not even comments or dates. XML is all text until a schema adds types. YAML guesses a type from how a value looks, so under YAML 1.1 rules no reads as false, while TOML quotes every string and guesses nothing.