Often as a developer, you want to simulate the experience of limited bandwidth for people with slower internet connections. Chrome and FireFox have this built into the browser, but it only affects the browser and doesn't provide robust parameters for latency or affect the rest of the experience. Safari doesn't have this, and it's in part to the Network Link Conditioner utility provided as an additional tool. To install the Network Link Conditioner, you'll need the following: Apple Developer account (no paid licensing is required)

Xcode installed Next, go to downloads for Apple Developers and sign in. The Network Link Conditioner utility is packaged in with other utilities. Search for Additional Tools or use one of the links below. OS X 10.10 users should download Hardware IO Tools for Xcode 7.3

OS X 10.10 users should download Additional Tools for Xcode 8.2

OS X 10.12 users should download Additional Tools for Xcode 9

Open up the DMG and install Network Link Conditioner.prefPane by double-clicking it. (Note: in Additional Tools, it'll likely be in the hardware folder)

Using Network Link Conditioner

Open up the system prefs on your computer. Click on Network Link Conditioner and click on/off to toggle it on, and the drop down to use presets. You can create your own with the Manage Profiles.

Congrats, now you can enjoy slow internet.