I would probably only say either -Ik maak maar een grapje. -Het is maar een grapje. Or simply 'Grapje!'

Here are some possible phrases: Ik lach er mee. Ik lach er maar mee. Ik maak een grapje. (Ik hou je voor de gek.)

Ik maak maar een grapje. Ik loop maar te dollen.

"I'm (just) kidding/joking" -> "Ik maak (maar) een grapje." "I am kidding/joking with you." -> "Ik zit je voor de gek te houden." (kind of: "I'm treating you like a fool, like someone crazy.") I don't know a good way to distinguish kidding and joking in Dutch. I don't have a good feel for the difference in English either. There's also "Ik maak maar een geintje." Geintje is derived from the noun "gein". "Een grap" is literally "a joke". "een gein" does not exist, because "gein" is uncountable. "gein" (again Dutch-Dutch) means fun, amusement. "geintje" is according to my dictionary "Nederlands-Nederlands" (i.e. Dutch-Dutch) so it may not be understood in Flanders. I think "een grapje" (or "een grap") is often on a verbal level (you deliberately twist the truth, or say something that's meant to be funny), Een geintje may be more physical, possibly involving your body or objects. Making a weird face or jumping in front of someone at an opportune moment. They're mostly synonyms I guess. I must say I'm not a big jester myself. Others may be able to comment better on the science of having fun with people.

Thanks Alicia I was asking 'DUTCH' Speaking people how do they say I am joking with you I am just Joking I am just kidding I am messing around. Do you know how to translate or whats the equivalent in 'DUTCH'. lol