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");
        }
    }
}