diff --git a/NearDrop/SelfTest/ApIsolation6Tester.swift b/NearDrop/SelfTest/ApIsolation6Tester.swift
new file mode 100644
index 0000000..54ef3f1
--- /dev/null
+++ b/NearDrop/SelfTest/ApIsolation6Tester.swift
@@ -0,0 +1,53 @@
+//
+//  ApIsolation6Tester.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 14.05.25.
+//
+
+import Foundation
+import Network
+
+class IPv6DeviceScanner {
+    /// Scans for IPv6 devices using `ping6 ff02::1` multicast on the given interface.
+    /// - Parameters:
+    ///   - interface: The interface to scan on (e.g. "en0").
+    ///   - timeout: How long to wait for replies (default 2 seconds).
+    ///   - completion: Callback with a list of detected device IPs (excluding router).
+    func scan(interface: String = "en0", timeout: TimeInterval = 2.0, completion: @escaping ([String]) -> Void) {
+        let process = Process()
+        process.executableURL = URL(fileURLWithPath: "/sbin/ping6")
+        process.arguments = ["-I", interface, "-c", "2", "ff02::1"]
+
+        let pipe = Pipe()
+        process.standardOutput = pipe
+        process.standardError = pipe
+
+        process.terminationHandler = { _ in
+            let data = pipe.fileHandleForReading.readDataToEndOfFile()
+            let output = String(data: data, encoding: .utf8) ?? ""
+
+            let lines = output
+                .components(separatedBy: "\n")
+                .filter { $0.contains("bytes from") }
+
+            let ips = lines.compactMap { line -> String? in
+                let match = line.components(separatedBy: " ").first(where: { $0.contains(":") && !$0.contains("ff02") })
+                return match?.trimmingCharacters(in: .punctuationCharacters)
+            }
+
+            // Heuristic: Router is often the first responder — exclude the first
+            let uniqueIPs = Array(Set(ips))
+            let withoutRouter = Array(uniqueIPs.dropFirst())
+
+            completion(withoutRouter)
+        }
+
+        do {
+            try process.run()
+        } catch {
+            print("Failed to run ping6: \(error)")
+            completion([])
+        }
+    }
+}
diff --git a/NearDrop/SelfTest/ApIsolationTester.swift b/NearDrop/SelfTest/ApIsolationTester.swift
new file mode 100644
index 0000000..cb420db
--- /dev/null
+++ b/NearDrop/SelfTest/ApIsolationTester.swift
@@ -0,0 +1,98 @@
+//
+//  ApIsolationTester.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 14.05.25.
+//
+
+import Foundation
+import Network
+
+class DeviceToDeviceHeuristicScanner {
+    private let scanQueue = DispatchQueue(label: "DeviceToDeviceScanQueue")
+    private var reachableIPs = [String]()
+    private var scannedCount = 0
+    private var totalToScan = 0
+    private var completion: ((Bool) -> Void)?
+    
+    /// Start scanning the subnet for reachable peers.
+    /// - Parameters:
+    ///   - baseSubnet: e.g. `"192.168.1"` — if nil, will auto-detect
+    ///   - completion: true if any peer device was reachable
+    func scan(subnet baseSubnet: String? = nil, port: UInt16 = 80, completion: @escaping (Bool) -> Void) {
+        self.completion = completion
+        let subnet = baseSubnet ?? Self.getLocalSubnetPrefix() ?? "192.168.1"
+        let ipsToScan = (2...20).map { "\(subnet).\($0)" }
+        totalToScan = ipsToScan.count
+        
+        for ip in ipsToScan {
+            testConnection(to: ip, port: port)
+        }
+
+        // Timeout fallback
+        DispatchQueue.main.asyncAfter(deadline: .now() + 6.0) {
+            if self.scannedCount < self.totalToScan {
+                self.finish()
+            }
+        }
+    }
+    
+    private func testConnection(to ip: String, port: UInt16) {
+        guard let nwPort = NWEndpoint.Port(rawValue: port) else { return }
+        let connection = NWConnection(host: NWEndpoint.Host(ip), port: nwPort, using: .tcp)
+
+        connection.stateUpdateHandler = { state in
+            switch state {
+            case .ready:
+                self.reachableIPs.append(ip)
+                connection.cancel()
+                self.hostFinished()
+            case .failed, .cancelled:
+                connection.cancel()
+                self.hostFinished()
+            default:
+                break
+            }
+        }
+
+        connection.start(queue: scanQueue)
+    }
+
+    private func hostFinished() {
+        scannedCount += 1
+        if scannedCount == totalToScan {
+            finish()
+        }
+    }
+
+    private func finish() {
+        completion?(reachableIPs.count > 0)
+    }
+
+    /// Attempts to detect the local subnet prefix (e.g., "192.168.0")
+    private static func getLocalSubnetPrefix() -> String? {
+        var ifaddr: UnsafeMutablePointer<ifaddrs>?
+        if getifaddrs(&ifaddr) == 0 {
+            var ptr = ifaddr
+            while ptr != nil {
+                defer { ptr = ptr!.pointee.ifa_next }
+                let interface = ptr!.pointee
+                let addrFamily = interface.ifa_addr.pointee.sa_family
+                if addrFamily == UInt8(AF_INET),
+                   let name = String(validatingUTF8: interface.ifa_name),
+                   name == "en0" || name == "en1" || name.contains("wlan") {
+                    var hostname = [CChar](repeating: 0, count: Int(NI_MAXHOST))
+                    getnameinfo(interface.ifa_addr, socklen_t(interface.ifa_addr.pointee.sa_len),
+                                &hostname, socklen_t(hostname.count), nil, 0, NI_NUMERICHOST)
+                    if let ip = String(validatingUTF8: hostname),
+                       let lastDot = ip.lastIndex(of: ".") {
+                        freeifaddrs(ifaddr)
+                        return String(ip[..<lastDot])
+                    }
+                }
+            }
+            freeifaddrs(ifaddr)
+        }
+        return nil
+    }
+}
diff --git a/NearDrop/SelfTest/FirewallTester.swift b/NearDrop/SelfTest/FirewallTester.swift
new file mode 100644
index 0000000..40ef30c
--- /dev/null
+++ b/NearDrop/SelfTest/FirewallTester.swift
@@ -0,0 +1,70 @@
+//
+//  FirewallTester.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 14.05.25.
+//
+
+import Foundation
+import Network
+
+
+class FirewallSelfTest {
+    private var listener: NWListener?
+    private var didReceiveResponse = false
+
+    func testLocalLoopbackConnection(timeout: TimeInterval = 3.0, completion: @escaping (Bool) -> Void) {
+        // Step 1: Create a listener on a random available port
+        do {
+            let parameters = NWParameters.tcp
+            listener = try NWListener(using: parameters, on: 0) // 0 = auto-select available port
+        } catch {
+            print("Failed to create listener: \(error)")
+            completion(false)
+            return
+        }
+
+        listener?.stateUpdateHandler = { newState in
+            if case .ready = newState {
+                // Step 2: Once listener is ready, connect to it via loopback
+                guard let port = self.listener?.port else {
+                    completion(false)
+                    return
+                }
+
+                let connection = NWConnection(host: "127.0.0.1", port: port, using: .tcp)
+                connection.stateUpdateHandler = { state in
+                    switch state {
+                    case .ready:
+                        self.didReceiveResponse = true
+                        connection.cancel()
+                        self.listener?.cancel()
+                        completion(true)
+                    case .failed, .cancelled:
+                        if !self.didReceiveResponse {
+                            completion(false)
+                        }
+                    default:
+                        break
+                    }
+                }
+
+                connection.start(queue: .main)
+            }
+        }
+
+        listener?.newConnectionHandler = { newConnection in
+            newConnection.cancel() // We just need to know we can connect
+        }
+
+        listener?.start(queue: .main)
+
+        // Step 3: Timeout fallback
+        DispatchQueue.main.asyncAfter(deadline: .now() + timeout) {
+            if !self.didReceiveResponse {
+                self.listener?.cancel()
+                completion(false)
+            }
+        }
+    }
+}
diff --git a/NearDrop/SelfTest/MdnsTester.swift b/NearDrop/SelfTest/MdnsTester.swift
new file mode 100644
index 0000000..6b866f1
--- /dev/null
+++ b/NearDrop/SelfTest/MdnsTester.swift
@@ -0,0 +1,52 @@
+//
+//  MdnsTester.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 14.05.25.
+//
+
+import Foundation
+
+class MDNSSelfTest: NSObject, NetServiceDelegate, NetServiceBrowserDelegate {
+    private var service: NetService?
+    private var browser: NetServiceBrowser?
+    private var didFindOwnService = false
+    private var completionHandler: ((Bool) -> Void)?
+
+    func testBonjourAvailability(timeout: TimeInterval = 5.0, completion: @escaping (Bool) -> Void) {
+        self.completionHandler = completion
+
+        // Step 1: Start advertising a Bonjour service
+        let serviceName = "MDNS-Test-\(UUID().uuidString.prefix(6))"
+        service = NetService(domain: "local.", type: "_mdnstest._tcp.", name: serviceName, port: 12345)
+        service?.delegate = self
+        service?.publish()
+
+        // Step 2: Start browsing for it
+        browser = NetServiceBrowser()
+        browser?.delegate = self
+        browser?.searchForServices(ofType: "_mdnstest._tcp.", inDomain: "local.")
+
+        // Step 3: Timeout if nothing is found
+        DispatchQueue.main.asyncAfter(deadline: .now() + timeout) {
+            self.stop()
+            self.completionHandler?(self.didFindOwnService)
+        }
+    }
+
+    func netServiceBrowser(_ browser: NetServiceBrowser, didFind service: NetService, moreComing: Bool) {
+        if service.name == self.service?.name {
+            didFindOwnService = true
+            stop()
+            completionHandler?(true)
+            completionHandler = nil
+        }
+    }
+
+    func stop() {
+        service?.stop()
+        browser?.stop()
+        service = nil
+        browser = nil
+    }
+}
diff --git a/NearDrop/SelfTest/SelfTestManager.swift b/NearDrop/SelfTest/SelfTestManager.swift
new file mode 100644
index 0000000..0f3a580
--- /dev/null
+++ b/NearDrop/SelfTest/SelfTestManager.swift
@@ -0,0 +1,69 @@
+//
+//  SelfTestManager.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 15.05.25.
+//
+
+import Foundation
+import Network
+
+class SelfTestManager {
+    
+    static func run() {
+        
+        let tester = FirewallSelfTest()
+        tester.testLocalLoopbackConnection { allowed in
+            if allowed {
+                print("✅ Incoming connections appear allowed (no firewall or allowed exception).")
+            } else {
+                print("❌ Incoming connections may be blocked (firewall or system policy).")
+            }
+        }
+        
+        let tester2 = MDNSSelfTest()
+        tester2.testBonjourAvailability { available in
+            if available {
+                print("✅ mDNS is working — multicast DNS responses received.")
+            } else {
+                print("❌ mDNS seems blocked — possibly by network or router settings.")
+            }
+        }
+        
+        let scanner = DeviceToDeviceHeuristicScanner()
+        scanner.scan { allowed in
+            if allowed {
+                print("✅ Device-to-device likely allowed (peer responded on LAN).")
+            } else {
+                
+                let scanner2 = IPv6DeviceScanner()
+                scanner2.scan(interface: "en0") { devices in
+                    if devices.isEmpty {
+                        print("❌ No local devices responded — peer-to-peer may be blocked.")
+                    } else {
+                        print("✅ Found IPv6 devices (excluding router):")
+                        for ip in devices {
+                            print("  • \(ip)")
+                        }
+                    }
+                }
+            }
+        }
+        
+        let port: UInt16 = 43210
+        let packetCount = 10  // 32K packets
+        let packetSize = 512 * 1024        // Each packet = UInt32
+        let totalSize = packetCount * packetSize
+
+        let server = TCPSelfTestServer()
+        let client = TCPSelfTestClient()
+
+        server.start(port: NWEndpoint.Port(rawValue: port)!, expectedPackets: packetCount) { success, report in
+            print(success ? "✅ Success: \(report)" : "❌ Failure: \(report)")
+        }
+
+        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
+            client.sendSequentialPackets(to: port, count: packetCount)
+        }
+    }
+}
diff --git a/NearDrop/SelfTest/TcpSelfTestClient.swift b/NearDrop/SelfTest/TcpSelfTestClient.swift
new file mode 100644
index 0000000..e555d68
--- /dev/null
+++ b/NearDrop/SelfTest/TcpSelfTestClient.swift
@@ -0,0 +1,38 @@
+//
+//  TcpSelfTestClient.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 14.05.25.
+//
+
+import Foundation
+import Network
+
+class TCPSelfTestClient {
+    func sendSequentialPackets(to port: UInt16, count: Int) {
+        guard let nwPort = NWEndpoint.Port(rawValue: port) else { return }
+
+        let connection = NWConnection(host: "127.0.0.1", port: nwPort, using: .tcp)
+        connection.stateUpdateHandler = { state in
+            if state == .ready {
+                var allData = Data()
+                for i in 0..<count {
+                    var value = UInt32(i).bigEndian
+                    let packet = Data(bytes: &value, count: 4)
+                    allData.append(packet)
+                }
+
+                connection.send(content: allData, completion: .contentProcessed { error in
+                    if let error = error {
+                        print("Client error: \(error)")
+                    } else {
+                        print("✅ Client sent \(count) packets")
+                    }
+                    connection.cancel()
+                })
+            }
+        }
+
+        connection.start(queue: .main)
+    }
+}
diff --git a/NearDrop/SelfTest/TcpSelfTestServer.swift b/NearDrop/SelfTest/TcpSelfTestServer.swift
new file mode 100644
index 0000000..c766b8b
--- /dev/null
+++ b/NearDrop/SelfTest/TcpSelfTestServer.swift
@@ -0,0 +1,82 @@
+//
+//  TcpSelfTestServer.swift
+//  QuickDrop
+//
+//  Created by Leon Böttger on 14.05.25.
+//
+
+import Foundation
+import Network
+
+class TCPSelfTestServer {
+    private var listener: NWListener?
+    private var receivedData = Data()
+    var onComplete: ((Bool, String) -> Void)?
+    private var expectedPackets: Int = 0
+
+    func start(port: NWEndpoint.Port, expectedPackets: Int, onComplete: @escaping (Bool, String) -> Void) {
+        self.onComplete = onComplete
+        self.expectedPackets = expectedPackets
+
+        do {
+            let listener = try NWListener(using: .tcp, on: port)
+            self.listener = listener
+            listener.newConnectionHandler = { connection in
+                connection.start(queue: .main)
+                self.receive(on: connection)
+            }
+            listener.start(queue: .main)
+        } catch {
+            onComplete(false, "Server failed: \(error.localizedDescription)")
+        }
+    }
+
+    private func receive(on connection: NWConnection) {
+        connection.receive(minimumIncompleteLength: 1, maximumLength: 64 * 1024) { data, _, isComplete, error in
+            if let data = data {
+                self.receivedData.append(data)
+            }
+
+            if isComplete || self.receivedData.count >= self.expectedPackets * 4 {
+                connection.cancel()
+                self.listener?.cancel()
+                self.verify()
+            } else if error == nil {
+                self.receive(on: connection)
+            } else {
+                self.onComplete?(false, "Receive error: \(String(describing: error))")
+            }
+        }
+    }
+
+    private func verify() {
+        var values = [UInt32]()
+        let total = receivedData.count / 4
+        for i in 0..<total {
+            let range = i*4..<i*4+4
+            let chunk = receivedData.subdata(in: range)
+            let value = chunk.withUnsafeBytes { $0.load(as: UInt32.self).bigEndian }
+            values.append(value)
+        }
+
+        let expected = Array(0..<UInt32(values.count))
+        let dropped = expected.filter { !values.contains($0) }
+        let duplicates = Dictionary(grouping: values, by: { $0 }).filter { $1.count > 1 }.keys
+
+        if !dropped.isEmpty || !duplicates.isEmpty || values != expected {
+            var issues = [String]()
+            if !dropped.isEmpty {
+                issues.append("Dropped packets: \(dropped.prefix(10))...")
+            }
+            if !duplicates.isEmpty {
+                issues.append("Duplicates: \(duplicates.prefix(10))")
+            }
+            if values != expected {
+                issues.append("Out-of-order delivery detected.")
+            }
+            onComplete?(false, issues.joined(separator: " | "))
+        } else {
+            onComplete?(true, "All packets received in order")
+        }
+    }
+}
diff --git a/QuickDrop.xcodeproj/project.pbxproj b/QuickDrop.xcodeproj/project.pbxproj
index 40238e4..a3054ad 100644
--- a/QuickDrop.xcodeproj/project.pbxproj
+++ b/QuickDrop.xcodeproj/project.pbxproj
@@ -228,6 +228,7 @@
 /* End PBXFileReference section */
 
 /* Begin PBXFileSystemSynchronizedRootGroup section */
+		EB1A7E422DD4D8BD00A6D5A3 /* SelfTest */ = {isa = PBXFileSystemSynchronizedRootGroup; explicitFileTypes = {}; explicitFolders = (); path = SelfTest; sourceTree = "<group>"; };
 		EB7CD13B2D6F8B6500CB0CB5 /* IAP */ = {isa = PBXFileSystemSynchronizedRootGroup; explicitFileTypes = {}; explicitFolders = (); path = IAP; sourceTree = "<group>"; };
 /* End PBXFileSystemSynchronizedRootGroup section */
 
@@ -315,6 +316,7 @@
 				69DA9A1129E0BF5100A442DA /* AppDelegate.swift */,
 				EBD2A2162D2860BE00BCB8E2 /* WelcomeScreen.swift */,
 				EB7F54112D78E95C00989564 /* TutorialView.swift */,
+				EB1A7E422DD4D8BD00A6D5A3 /* SelfTest */,
 				EB7F54132D78E9E400989564 /* LicenseWindow.swift */,
 				EB6F62D62D91F4AC00534EC2 /* SettingsView.swift */,
 				EB36435F2D73A29F009CDFF8 /* AudioManager.swift */,
@@ -422,6 +424,7 @@
 				69DCF4972AB8BF7B00CBE2CC /* PBXTargetDependency */,
 			);
 			fileSystemSynchronizedGroups = (
+				EB1A7E422DD4D8BD00A6D5A3 /* SelfTest */,
 				EB7CD13B2D6F8B6500CB0CB5 /* IAP */,
 			);
 			name = QuickDrop;