Introducing Peek 2.0


Peek is an open source library that lets you easily check your application against your user interface’s specification guide(s). Peek can be used by engineers, designers & testers, allowing developers to spend more time on code and less time checking that fonts, colors and layout are pixel perfect.

How does it work?

Tap your volume key(s) to activate/deactivate Peek.

Then tap, or drag your finger across the screen to select a component and see its layout information.

Double-tap anywhere on the screen to bring up the Peek Inspectors. Here peek will show you contextual information about the view you’re inspecting. For example, a label will show information such as font and textColor, whereas an image might show information about its size or scaling mode.

You can also tap and hold on any property to copy it to your pasteboard. More features coming soon regarding this — which will allow you to report issues back to your dev(s).

Peek currently supports a single overlay mode, but more are coming soon – including an overlay that allows you to see measures between components!

How do I get started?

Peek was designed to be extremely easy to use.

If you’re a designer, send a link to this page to your dev(s) 😁

For developers, simply use CocoaPods (alternativel you can simply drag the files into your project.

pod 'Peek'

Then add a single line to your App Delegate:

window?.peek.enabled = true

Optionally, I’d suggest adding the DEBUG Swift compiler flag and changing the code to:

  window?.peek.enabled = true

You can also provide options when enabling Peek:

window?.peek.enableWithOptions { options in
  // Peek will require a shake on the device and simulator
  options.activationMode = .shake

  // Container views (UIView) will not be ignored
  // Note: this does not include system containers
  options.shouldIgnoreContainers = false

Now whenever you run your app, you can now activate/deactivate Peek by pressing one of the volume keys on your device 😉

Safety First

Peek is designed to be as safe as possible. Peek will never retain objects from your application. It will never use a background thread. Peek won’t even run unless you explicitly enable it!

Go ahead, take a Peek at your app now 🙂

What about using Peek from the simulator?

Since the volume keys are not available on the Simulator, we can use a shake gesture instead. Simply forward the motion events to Peek by adding the following code to your AppDelegate.swift:

override func motionBegan(motion: UIEventSubtype, withEvent event: UIEvent?) {

Now you can press CMD+CTRL+Z (or use the Menu option) to activate/deactivate Peek from your Simulator.

Supported Platforms and Versions

Peek is tested and supported on iOS 8 and above. Its also iPhone and iPad supported, in all orientations. In fact, Peek will only rotate if your app can 😉

About Peek

  1. Peek only requires a single line of code to get started
  2. Peek is disabled by default, so just make sure to use #if DEBUG to prevent it from being included in your release binary
  3. No 3rd party code or libraries are used in Peek — all code is my own!
  4. Peek never interferes with your apps normal behavior, gestures or layout – and it NEVER retains an object from your application
  5. Peek supports all orientations and devices.

How does Peek work?

Peek scans all the views in your entire view hierarchy that is currently on the screen then overlays these views with layout information.

Peek then uses its filtering system to best determine which views you care about and those that you are not likely to be interested in.

For example, by default Peek will not show you many of Apple’s system components unless they are subclassed. A label however is a perfect exception to this, where you might not want to see all labels in a tab-bar but you do want to see the labels inside a cell.

Peek presents itself in its own window that sits directly on top of your own app’s user interface to ensure that it doesn’t interfere with normal functionality.

Peek also allows you to test all supported orientations on both iPhone and iPad.


There are a lot more features still to come, here’s a short preview I think are quite interesting:

  • Slack Integration (post issues to a Slack channel)
  • Image crop indicators
  • Auto Layout overlays