taplo is a CLI tool (and a Rust library) for working with TOML. It can check TOML files for syntax errors, validate them against JSON schemas, and format.

The best thing about it is the Even Better TOML VSCode plugin wrapping taplo that provides all the same things as CLI plus smart syntax highlighting, navigation, refactoring, and even autocomplete for pyproject.toml, fly.toml, Cargo.toml and a few other formats.