StopwatchAttribute.cs

using System;
using System.Web;
using System.Web.Mvc;
using System.Diagnostics;


/// <summary>
/// A simple attribute that times controller actions, returning the measured time
/// in the HTTP header "X-Duration".
/// </summary>
public class StopwatchAttribute : ActionFilterAttribute
{
    private Stopwatch _stopwatch;

    public StopwatchAttribute()
    {
        _stopwatch = new Stopwatch();
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        _stopwatch.Start();
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        HttpResponseBase response = filterContext.HttpContext.Response;

        _stopwatch.Stop();

        response.AppendHeader("X-Duration", string.Format("{0}ms", _stopwatch.ElapsedMilliseconds));

        _stopwatch.Reset();
    }
}