What is the correct way to determine type of string, xml, json, delimiter, name/value pair etc

How to determine type of string?

It can be either the following type types

1) Name/Value Pair

2) Delimiter

3) XML

4) JSON

5) Unknown (invalid)

public string GetValueByName (string Name)
{
  //determine string type
  //return the value
}

Is it ok if we did this for 3 (json), 4 (xml)?

For XML we can check if the first character is <, then we check if XML is valid
For JSON we can check if the first character is {, then we check if JSON is valid