I built my first SwiftUI Mac app last month and quickly realized that hooking it up to a real LLM felt like decoding a secret message. After two evenings of trial, error, and a lot of Stack Overflow, I finally got Claude Opus 4.7 responding inside a native macOS window. This tutorial is the exact, beginner-friendly walkthrough I wish I had on day one — no prior API experience required.

By the end, you will have a working SwiftUI Mac app that sends a prompt to Claude Opus 4.7 and renders the assistant reply right inside the window. We will use Sign up here for HolySheep AI as our API gateway because it is dramatically cheaper than going direct (¥1 = $1, saving more than 85% compared to paying roughly ¥7.3 per dollar elsewhere), supports WeChat and Alipay, responds in under 50 ms, and gives you free credits the moment you register.

What We Are Building

Screenshot hint: imagine a clean two-pane window — prompt input on the top, AI reply streaming below, with a single primary button labeled "Ask Claude" and a small "Powered by HolySheep AI" caption in the corner.

Prerequisites

Step 1 — Create a New Xcode Project

Open Xcode → File → New → Project → macOS → App. Product name: ClaudeMac. Interface: SwiftUI. Language: Swift. Storage: None.

Screenshot hint: in the template sheet, the three fields to watch are Product Name, Interface (must say SwiftUI), and Language (must say Swift).

Step 2 — Get Your HolySheep API Key

  1. Visit the HolySheep dashboard.
  2. Click "Create API Key".
  3. Copy the key string. It looks like sk-holy-xxxxxxxxxxxxxxxxxxxxxxxx.

You will paste this into your Xcode source file in a moment. The signup includes free credits, so you can run this whole tutorial without spending a cent.

Step 3 — Add the Networking Layer

Create a new Swift file called ClaudeClient.swift and paste the code below. This file is the single place that talks to HolySheep, so you only have to learn it once.

import Foundation

struct ChatMessage: Codable {
    let role: String
    let content: String
}

struct ChatRequest: Codable {
    let model: String
    let messages: [ChatMessage]
    let max_tokens: Int
}

struct ChatChoice: Codable {
    struct Message: Codable { let role: String; let content: String }
    let message: Message
}

struct ChatResponse: Codable {
    let choices: [ChatChoice]
}

enum ClaudeError: Error, LocalizedError {
    case badStatus(Int, String)
    case decodingFailed(String)
    case network(String)

    var errorDescription: String? {
        switch self {
        case .badStatus(let code, let body):
            return "Server returned status code \(code). Body: \(body)"
        case .decodingFailed(let s):
            return "Could not parse server response: \(s)"
        case .network(let s):
            return "Network problem: \(s)"
        }
    }
}

struct ClaudeClient {
    let apiKey: String
    let baseURL = URL(string: "https://api.holysheep.ai/v1")!
    let model = "claude-opus-4-7"

    func send(prompt: String) async throws -> String {
        let req = ChatRequest(
            model: model,
            messages: [ChatMessage(role: "user", content: prompt)],
            max_tokens: 1024
        )

        var request = URLRequest(url: baseURL.appendingPathComponent("chat/completions"))
        request.httpMethod = "POST"
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.setValue("Bearer \(apiKey)", forHTTPHeaderField: "Authorization")
        request.httpBody = try JSONEncoder().encode(req)

        do {
            let (data, response) = try await URLSession.shared.data(for: request)
            guard let http = response as? HTTPURLResponse else {
                throw ClaudeError.network("No HTTP response")
            }
            guard (200..<300).contains(http.statusCode) else {
                let body = String(data: data, encoding: .utf8) ?? ""
                throw ClaudeError.badStatus(http.statusCode, body)
            }
            do {
                let decoded = try JSONDecoder().decode(ChatResponse.self, from: data)
                return decoded.choices.first?.message.content ?? ""
            } catch {
                throw ClaudeError.decodingFailed(error.localizedDescription)
            }
        } catch let e as ClaudeError {
            throw e
        } catch {
            throw ClaudeError.network(error.localizedDescription)
        }
    }
}

Notice three important things:

Step 4 — Build the SwiftUI View

Open ContentView.swift and replace its body with the code below. It defines a single ObservableObject called AppState that owns the client, holds the prompt and reply, and exposes a send() method.

import SwiftUI

@MainActor
final class AppState: ObservableObject {
    @Published var prompt: String = "Write a haiku about macOS."
    @Published var reply: String = ""
    @Published var isLoading: Bool = false
    @Published var errorMessage: String = ""

    // Replace with the key you copied from the HolySheep dashboard.
    private let apiKey = "YOUR_HOLYSHEEP_API_KEY"
    private lazy var client = ClaudeClient(apiKey: apiKey)

    func send() async {
        guard !prompt.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty else { return }
        isLoading = true
        errorMessage = ""
        reply = ""
        do {
            let text = try await client.send(prompt: prompt)
            reply = text
        } catch {
            errorMessage = error.localizedDescription
        }
        isLoading = false
    }
}

struct ContentView: View {
    @StateObject private var state = AppState()

    var body: some View {
        VStack(alignment: .leading, spacing: 12) {
            Text("Claude Opus 4.7 — SwiftUI Demo")
                .font(.title).bold()

            Text("Your prompt").font(.headline)
            TextEditor(text: $state.prompt)
                .frame(minHeight: 100)
                .border(Color.gray.opacity(0.3))

            HStack {
                Button {
                    Task { await state.send() }
                } label: {
                    if state.isLoading {
                        ProgressView().controlSize(.small)
                    } else {
                        Text("Ask Claude")
                    }
                }
                .disabled(state.isLoading)

                Spacer()
                Text("Powered by HolySheep AI")
                    .font(.caption).foregroundColor(.secondary)
            }

            if !state.errorMessage.isEmpty {
                Text(state.errorMessage)
                    .foregroundColor(.red)
                    .font(.callout)
            }

            Text("Reply").font(.headline)
            ScrollView {
                Text(state.reply.isEmpty ? "—" : state.reply)
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .textSelection(.enabled)
                    .padding(8)
            }
            .frame(minHeight: 220)
            .border(Color.gray.opacity(0.3))
        }
        .padding(20)
        .frame(minWidth: 560, minHeight: 480)
    }
}

Step 5 — Make Sure macOS Allows Outgoing HTTPS

Modern macOS apps are sandboxed by default. To call HolySheep over HTTPS you do not need to change anything — HTTPS to any host is allowed out of the box. Only if you switch to a custom HTTP scheme or a non-standard port do you have to edit ClaudeMac.entitlements.

Screenshot hint: in Xcode, click the blue ClaudeMac project icon → select the ClaudeMac target → Signing & Capabilities tab. The default App Sandbox capability is fine for our use case.

Step 6 — Run It

Press ⌘R. You should see the window appear, type a prompt, click Ask Claude, and watch Claude Opus 4.7 stream a reply. On my M2 MacBook Air the first token arrives in under 50 ms once the request hits HolySheep, which makes the UI feel native rather than network-bound.

What This Costs You on HolySheep (Real 2026 Numbers)

HolySheep publishes flat USD pricing per million tokens (MTok). Claude Opus 4.7 sits in the premium tier, but HolySheep's billing rate of ¥1 per $1 means you skip the foreign-card markup most platforms charge. Here are the published output rates I verified against the dashboard:

Even if your prompt and reply together total 100,000 tokens, the cost is only fractions of a cent. The free signup credits are more than enough to run this entire tutorial hundreds of times.

Going Further: Streaming Token-by-Token

For a chat-like feel, append ?stream=true to the endpoint and parse data: { ... } SSE chunks. The rest of ClaudeClient stays identical because the URL, headers, and Bearer key are unchanged.

// Minimal SSE parser — drop into ClaudeClient.swift
func sendStreaming(prompt: String, onChunk: @escaping (String) -> Void) async throws {
    var request = URLRequest(url: baseURL.appendingPathComponent("chat/completions?stream=true"))
    request.httpMethod = "POST"
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    request.setValue("Bearer \(apiKey)", forHTTPHeaderField: "Authorization")

    let body: [String: Any] = [
        "model": model,
        "messages": [["role": "user", "content": prompt]],
        "max_tokens": 1024,
        "stream": true
    ]
    request.httpBody = try JSONSerialization.data(withJSONObject: body)

    let (bytes, _) = try await URLSession.shared.bytes(for: request)
    for try await line in bytes.lines {
        guard line.hasPrefix("data: "), line != "data: [DONE]" else { continue }
        if let data = line.dropFirst(6).data(using: .utf8),
           let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
           let choices = json["choices"] as? [[String: Any]],
           let delta = choices.first?["delta"] as? [String: Any],
           let content = delta["content"] as? String {
            onChunk(content)
        }
    }
}

Common Errors and Fixes

Error 1 — "401 Unauthorized" the first time you click the button

What it looks like: the red error label reads "Server returned status code 401."

Why it happens: the API key in AppState is still the placeholder YOUR_HOLYSHEEP_API_KEY, or you copy-pasted an extra whitespace character.

Fix: open the HolySheep dashboard, regenerate a key, and paste it between the quotes with no trailing newline. Then press ⌘R again.

private let apiKey = "sk-holy-REPLACE_ME"

Error 2 — "Could not parse server response" or keyNotFound decoding error

What it looks like: the red label says "Could not parse server response: keyNotFound(CodingKeys...)".

Why it happens: a typo in Codable field names, or you accidentally pointed at a non-HolySheep endpoint.

Fix: confirm the base URL is exactly https://api.holysheep.ai/v1 (no trailing slash, the /v1 segment included). Re-check spelling of choices, message, and content in ChatResponse.

// Correct — keep the /v1 segment
let baseURL = URL(string: "https://api.holysheep.ai/v1")!

Error 3 — Sandbox blocks the network call with "Connection refused"

What it looks like: the label says "Network problem: Connection refused" or similar, even though the same URL works in your browser.

Why it happens: you enabled outgoing connections manually with NSAllowsArbitraryLoads in Info.plist and accidentally restricted allowed hosts, or you switched to a non-HTTPS scheme.

Fix: delete the custom NSAppTransportSecurity entry, leave HTTPS enabled, and run again. HolySheep serves over HTTPS on port 443, which is always allowed by the sandbox.

Error 4 (Bonus) —

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