When you develop websites or apps your server is usually inside a local network or even in your own computer. To get a closer look to the real user experience you need to slow your network speed down. This is called network throttling and in Mac OS is really easy to do.

Mac OS

Head over to the downloads page in Apple's developer site and search for Hardware IO Tools

If you have Xcode, you can get to the downloads page through Xcode > Open developer tool > More developer tools

Download the latest image, open it and you will find a file called Network Link Conditioner.prefPane. Double-click it and will be added to your system preferences panel.

Now you can open the Network Link Conditioner in your system preferences and select the connection you want to simulate.

Do it, test how your site really behaves using a 3G connection or normal broadband, it might not render as fast as you thought. In addition, this is a great way to make sure you avoid race conditions.

iOS

Enable your device for development and a Developer item will pop up in Settings, allowing you to enable the network link conditioner, among other features.

Credits

I recently read @dschneller's comment in this post about simulating latency in Linux with tc and decided to elaborate on it, finally got some time to write a post here! :-)