Application.isPlaying

Description

Returns true when called in any kind of built Player, or when called in the Editor in Play Mode (Read Only).

In a built Player, this method always returns true.

In the Editor, it returns true if the Editor is in Play mode.

Note: In the Editor for ScriptableObject assets, this property returns false in OnEnable. After reloading the ___domain, when reloading assemblies, Unity invokes OnEnable on all ScriptableObject instances. This happens before isPlaying is set to true.

Additional resources: Application.IsPlaying, ExecuteAlways.

using UnityEngine;

class Example : MonoBehaviour
{
    void Start()
    {
        if (Application.isPlaying)
        {
            print("In player or playmode");
        }
    }
}