StringFormatQ
StringFormatQ["string","fmt"] gives True if the string "string" might be imported as format "fmt" and gives False otherwise.
StringFormatQ["string",{fmt1,fmt2,…}] gives True if "string" might be imported as one of "fmti".
Examples
StringFormatQ["{\"key\": 1}", "JSON"]
(* True *)StringFormatQ["<html></html>", {"JSON", "HTML"}]
(* True *)Please visit the official Wolfram Language Reference for more details.