Application.isEditor

static var isEditor : boolean

Description

Are we running inside the Unity editor? (Read Only)

Returns true if the game is being run from the Unity editor; false if run from any deployment target.

JavaScript
    if (Application.isEditor) {
print("We are running this from inside of the editor!");
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Example() {
if (Application.isEditor)
print("We are running this from inside of the editor!");

}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Example():
if Application.isEditor:
print('We are running this from inside of the editor!')