diff --git a/.github/workflows/check.yaml b/.github/workflows/check.yaml
index 5f7d29b..499c88b 100644
--- a/.github/workflows/check.yaml
+++ b/.github/workflows/check.yaml
@@ -59,6 +59,5 @@ jobs:
         with:
           xcode-version: ${{ matrix.tooling.xcode-version }}
 
-      # TODO OS version, and ambiguity in platforms, and no match
-      - run: xcodebuild -scheme AblyChat -destination "platform=${{ matrix.platform }}" SWIFT_TREAT_WARNINGS_AS_ERRORS=YES SWIFT_VERSION=${{ matrix.tooling.swift-version }}
-      - run: xcodebuild test -scheme AblyChat -destination "platform=${{ matrix.platform }}" SWIFT_TREAT_WARNINGS_AS_ERRORS=YES SWIFT_VERSION=${{ matrix.tooling.swift-version }}
+      - run: swift run BuildTool --platform ${{ matrix.platform }} --swift-version ${{ matrix.swift-version }}
+        working-directory: ./script
diff --git a/Package.resolved b/Package.resolved
index e3dae42..e65ca60 100644
--- a/Package.resolved
+++ b/Package.resolved
@@ -1,5 +1,5 @@
 {
-  "originHash" : "bb9e762d580eaf6bdfc4c2b4ef738357fe7528fca621f88bf37eab5f324406ae",
+  "originHash" : "10b6989ad831255bec51a3b6a49da12c471d57a9611e6834de10ee5a8863e652",
   "pins" : [
     {
       "identity" : "ably-cocoa",
@@ -28,15 +28,6 @@
         "version" : "0.4.0"
       }
     },
-    {
-      "identity" : "swift-argument-parser",
-      "kind" : "remoteSourceControl",
-      "location" : "https://github.com/apple/swift-argument-parser",
-      "state" : {
-        "revision" : "41982a3656a71c768319979febd796c6fd111d5c",
-        "version" : "1.5.0"
-      }
-    },
     {
       "identity" : "swiftformat",
       "kind" : "remoteSourceControl",
diff --git a/Package.swift b/Package.swift
index d02d79f..7c7c21c 100644
--- a/Package.swift
+++ b/Package.swift
@@ -21,7 +21,6 @@ let package = Package(
         .package(url: "https://github.com/ably/ably-cocoa", from: "1.2.0"),
         .package(url: "https://github.com/SimplyDanny/SwiftLintPlugins", from: "0.55.1"),
         .package(url: "https://github.com/nicklockwood/SwiftFormat", from: "0.54.0"),
-        .package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
     ],
     targets: [
         // Targets are the basic building blocks of a package, defining a module or a test suite.
@@ -33,6 +32,5 @@ let package = Package(
             name: "AblyChatTests",
             dependencies: ["AblyChat"]
         ),
-        .executableTarget(name: "TestScript", dependencies: [.product(name: "ArgumentParser", package: "swift-argument-parser")], swiftSettings: [.enableUpcomingFeature("StrictConcurrency")]),
     ]
 )
diff --git a/Sources/TestScript/GetDestination.swift b/Sources/TestScript/GetDestination.swift
deleted file mode 100644
index 0e35899..0000000
--- a/Sources/TestScript/GetDestination.swift
+++ /dev/null
@@ -1,83 +0,0 @@
-import ArgumentParser
-import Foundation
-
-struct SimctlOutput: Codable {
-    var devices: [String: [Device]]
-
-    struct Device: Codable {
-        var udid: String
-        var deviceTypeIdentifier: String
-    }
-}
-
-@main
-struct GetDestination: ParsableCommand {
-    static var configuration = CommandConfiguration(abstract: "Finds a simulator device matching given parameters, and writes its UUID to standard output.")
-
-    @Option(help: "The part of the runtime identifier that comes after \"com.apple.CoreSimulator.SimRuntime.\". For example, \"iOS-17-4\".")
-    var runtime: String
-
-    @Option(help: "The part of the device type identifier that comes after \"com.apple.CoreSimulator.SimDeviceType\". For example, \"iPhone-15\".")
-    var deviceType: String
-
-    mutating func run() throws {
-        let simctlOutput = try fetchSimctlOutput()
-
-        let runtimeIdentifier = "com.apple.CoreSimulator.SimRuntime.\(runtime)"
-        let deviceTypeIdentifier = "com.apple.CoreSimulator.SimDeviceType.\(deviceType)"
-        guard let matchingDevices = simctlOutput.devices[runtimeIdentifier]?.filter({ $0.deviceTypeIdentifier == deviceTypeIdentifier }) else {
-            fatalError("Couldn’t find a simulator with runtime \(runtimeIdentifier) and device type \(deviceTypeIdentifier); available devices are \(simctlOutput.devices)")
-        }
-
-        if matchingDevices.count > 1 {
-            fatalError("Found multiple simulators with runtime \(runtimeIdentifier) and device type \(deviceTypeIdentifier); matching devices are \(matchingDevices)")
-        }
-
-        print(matchingDevices[0].udid)
-    }
-
-    func fetchSimctlOutput() throws -> SimctlOutput {
-        let data = try runAndReturnStdout(
-            processPath: "/usr/bin/env",
-            arguments: ["xcrun", "simctl", "list", "--json"]
-        )
-
-        return try JSONDecoder().decode(SimctlOutput.self, from: data)
-    }
-
-    // I would have liked to use Swift concurrency for this but it felt like it would be a bit of a faff and it’s only a script. There’s a proposal for a Subprocess API coming up in Foundation which will marry Process with Swift concurrency.
-    private func runAndReturnStdout(processPath: String, arguments: [String]) throws -> Data {
-        let process = Process()
-        process.executableURL = URL(fileURLWithPath: processPath)
-        process.arguments = arguments
-
-        let standardOutput = Pipe()
-        process.standardOutput = standardOutput
-
-        let semaphore = DispatchSemaphore(value: 0)
-
-        process.terminationHandler = { _ in
-            semaphore.signal()
-        }
-
-        try process.run()
-
-        var stdoutData = Data()
-        while true {
-            if #available(macOS 14, *) {
-                if let data = try standardOutput.fileHandleForReading.readToEnd() {
-                    stdoutData.append(data)
-                } else {
-                    break
-                }
-            } else {
-                // TODO: this is annoying, we are stuck with the deployment target of the library
-                fatalError("Expected to be running on macOS 14")
-            }
-        }
-
-        semaphore.wait()
-
-        return stdoutData
-    }
-}
diff --git a/script/Package.resolved b/script/Package.resolved
new file mode 100644
index 0000000..62310a4
--- /dev/null
+++ b/script/Package.resolved
@@ -0,0 +1,15 @@
+{
+  "originHash" : "422fe248db2d0a796fdbfcd73b31069c259a3cc7bfb84dd769af3bd9c6fd84c4",
+  "pins" : [
+    {
+      "identity" : "swift-argument-parser",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-argument-parser",
+      "state" : {
+        "revision" : "41982a3656a71c768319979febd796c6fd111d5c",
+        "version" : "1.5.0"
+      }
+    }
+  ],
+  "version" : 3
+}
diff --git a/script/Package.swift b/script/Package.swift
new file mode 100644
index 0000000..a567a50
--- /dev/null
+++ b/script/Package.swift
@@ -0,0 +1,19 @@
+// swift-tools-version: 5.10
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+// TODO: explain why a separate package
+
+let package = Package(
+    name: "AblyChatBuildTools",
+    platforms: [
+        .macOS(.v14),
+    ],
+    dependencies: [
+        .package(url: "https://github.com/apple/swift-argument-parser", from: "1.5.0"),
+    ],
+    targets: [
+        .executableTarget(name: "BuildTool", dependencies: [.product(name: "ArgumentParser", package: "swift-argument-parser")], swiftSettings: [.enableUpcomingFeature("StrictConcurrency")]),
+    ]
+)
diff --git a/script/Sources/BuildTool/BuildTool.swift b/script/Sources/BuildTool/BuildTool.swift
new file mode 100644
index 0000000..f07b994
--- /dev/null
+++ b/script/Sources/BuildTool/BuildTool.swift
@@ -0,0 +1,167 @@
+import ArgumentParser
+import Foundation
+
+struct DestinationPredicate {
+    // TODO: document
+    var runtime: String
+    var deviceType: String
+}
+
+enum Platform: String {
+    case macOS
+    case iOS
+    case tvOS
+
+    // TODO: why is xcodebuild giving locally with iOS "--- xcodebuild: WARNING: Using the first of multiple matching destinations:"
+    var destinationPredicate: DestinationPredicate? {
+        switch self {
+        case .macOS: nil
+        case .iOS: .init(runtime: "iOS-17-4", deviceType: "iPhone-15")
+        case .tvOS: .init(runtime: "tvOS", deviceType: "TODO")
+        }
+    }
+}
+
+extension Platform: ExpressibleByArgument {
+    init?(argument: String) {
+        self.init(rawValue: argument)
+    }
+}
+
+struct SimctlOutput: Codable {
+    var devices: [String: [Device]]
+
+    struct Device: Codable {
+        var udid: String
+        var deviceTypeIdentifier: String
+    }
+}
+
+enum Error: Swift.Error {
+    case terminatedWithExitCode(Int32)
+}
+
+@main
+struct BuildTool: ParsableCommand {
+    @Option
+    var platform: Platform
+
+    @Option
+    var swiftVersion: Int
+
+    mutating func run() throws {
+        print("got platform \(platform)")
+        let deviceUDID: String? = if let destinationPredicate = platform.destinationPredicate {
+            try fetchDeviceUDID(destinationPredicate: destinationPredicate)
+        } else {
+            nil
+        }
+
+        // This tool runs from the repo’s `script` directory, so change into the repo root
+        FileManager.default.changeCurrentDirectoryPath("..")
+        try runXcodebuild(action: nil, deviceUDID: deviceUDID)
+        try runXcodebuild(action: "test", deviceUDID: deviceUDID)
+    }
+
+    func runXcodebuild(action: String?, deviceUDID: String?) throws {
+        var arguments: [String] = []
+
+        if let action {
+            arguments.append(action)
+        }
+
+        arguments.append(contentsOf: ["-scheme", "AblyChat"])
+
+        if let deviceUDID {
+            arguments.append(contentsOf: ["-destination", "id=\(deviceUDID)"])
+        }
+
+        arguments.append(contentsOf: [
+            "SWIFT_TREAT_WARNINGS_AS_ERRORS=YES",
+            "SWIFT_VERSION=\(swiftVersion)",
+        ])
+
+        try run(executableName: "xcodebuild", arguments: arguments)
+    }
+
+    func fetchDeviceUDID(destinationPredicate: DestinationPredicate) throws -> String {
+        let simctlOutput = try fetchSimctlOutput()
+
+        let runtimeIdentifier = "com.apple.CoreSimulator.SimRuntime.\(destinationPredicate.runtime)"
+        let deviceTypeIdentifier = "com.apple.CoreSimulator.SimDeviceType.\(destinationPredicate.deviceType)"
+        guard let matchingDevices = simctlOutput.devices[runtimeIdentifier]?.filter({ $0.deviceTypeIdentifier == deviceTypeIdentifier }) else {
+            fatalError("Couldn’t find a simulator with runtime \(runtimeIdentifier) and device type \(deviceTypeIdentifier); available devices are \(simctlOutput.devices)")
+        }
+
+        if matchingDevices.count > 1 {
+            fatalError("Found multiple simulators with runtime \(runtimeIdentifier) and device type \(deviceTypeIdentifier); matching devices are \(matchingDevices)")
+        }
+
+        return matchingDevices[0].udid
+    }
+
+    func fetchSimctlOutput() throws -> SimctlOutput {
+        let data = try runAndReturnStdout(
+            executableName: "xcrun",
+            arguments: ["simctl", "list", "--json"]
+        )
+
+        return try JSONDecoder().decode(SimctlOutput.self, from: data)
+    }
+
+    // I would have liked to use Swift concurrency for this but it felt like it would be a bit of a faff and it’s only a script. There’s a proposal for a Subprocess API coming up in Foundation which will marry Process with Swift concurrency.
+    private func run(executableName: String, arguments: [String]) throws {
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: "/usr/bin/env")
+        process.arguments = [executableName] + arguments
+
+        let semaphore = DispatchSemaphore(value: 0)
+
+        process.terminationHandler = { _ in
+            semaphore.signal()
+        }
+
+        try process.run()
+
+        semaphore.wait()
+
+        if process.terminationStatus != 0 {
+            throw Error.terminatedWithExitCode(process.terminationStatus)
+        }
+    }
+
+    // I would have liked to use Swift concurrency for this but it felt like it would be a bit of a faff and it’s only a script. There’s a proposal for a Subprocess API coming up in Foundation which will marry Process with Swift concurrency.
+    private func runAndReturnStdout(executableName: String, arguments: [String]) throws -> Data {
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: "/usr/bin/env")
+        process.arguments = [executableName] + arguments
+
+        let standardOutput = Pipe()
+        process.standardOutput = standardOutput
+
+        let semaphore = DispatchSemaphore(value: 0)
+
+        process.terminationHandler = { _ in
+            semaphore.signal()
+        }
+
+        try process.run()
+
+        var stdoutData = Data()
+        while true {
+            if let data = try standardOutput.fileHandleForReading.readToEnd() {
+                stdoutData.append(data)
+            } else {
+                break
+            }
+        }
+
+        semaphore.wait()
+
+        if process.terminationStatus != 0 {
+            throw Error.terminatedWithExitCode(process.terminationStatus)
+        }
+
+        return stdoutData
+    }
+}