Since the Mac App Store only hosts the most recent version of Xcode, you must use the Apple Developer Portal to access legacy versions. Resources - Xcode - Apple Developer

This is where the process gets tricky. You will not find Xcode 7.3.1 in the standard "Updates" tab of the Mac App Store. Apple removes older versions from the main store to encourage developers to stay current.

Installation:

If you run into a missing libarclite or Swift 2.3 compiler errors, you’ll need to adjust your project settings — but that’s a separate troubleshooting guide.

sudo xattr -d com.apple.quarantine /Applications/Xcode.app

Download the same way from the Apple Developer portal. Search for: Command Line Tools (OS X 10.11) for Xcode 7.3.1

sudo xcode-select -s /Applications/Xcode-7.3.1.app/

macOS Gatekeeper blocking an older, notarized binary.

| Requirement | Specification | | :--- | :--- | | | OS X El Capitan 10.11.5 or later (10.11.6 recommended) | | RAM | Minimum 2 GB (4 GB+ recommended for Simulator) | | Storage | At least 10 GB free (Xcode + additional components) | | Apple ID | Free Apple ID (for Apple Developer portal access) |

: This version includes the Swift 2.2 compiler.