Gradual, like TypeScript
Every valid .tex file is a valid ExactTeX document. Annotate one identifier and exactly that pair is checked; the coverage number tells you how much of the document is under contract.
Know whether your document is sound before you look at the PDF.
A document language with LaTeX as its backend. Rename your .tex and it keeps working — what you annotate is guaranteed by a compiler.
Errors in your own words
A closed table of fourteen hard errors, each at the site where the fix belongs — with the declaration it points at, one click away.
Revisions inside the file
@add, @del, @sub and @note live in the document. Any tool reads the same anchored changes; an agent suggests, a human accepts.
Three doors, one answer
CLI, language server and WebAssembly build share one core, and a parity suite holds them byte-for-byte to the same output.
References checked against the world
Bibliography entries, URLs, DOIs and repositories verified against live sources — a separate step writes a dated record, and the compiler replays it offline. The network never enters a compile.