OrderedQ

OrderedQ[h[e1, e2, …]] gives True if the ei are in canonical order, and False otherwise.

OrderedQ[h[e1, e2, …], p] uses the ordering function p.

Examples

Check canonical order:

OrderedQ[{a, b, c}]
(* True *)

Not in order:

OrderedQ[{c, a, b}]
(* False *)

Please visit the official Wolfram Language Reference for more details.