diff --git a/apps/desktop/src/setup.html b/apps/desktop/src/setup.html
new file mode 100644
index 0000000..a4e81aa
--- /dev/null
+++ b/apps/desktop/src/setup.html
@@ -0,0 +1,254 @@
+<!DOCTYPE html>
+<html lang="de">
+<head>
+  <meta charset="UTF-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <title>Tessera - Setup</title>
+  <style>
+    * {
+      margin: 0;
+      padding: 0;
+      box-sizing: border-box;
+    }
+
+    body {
+      font-family: "Inter", system-ui, -apple-system, sans-serif;
+      display: flex;
+      justify-content: center;
+      align-items: center;
+      min-height: 100vh;
+      background: oklch(0.17 0.01 260);
+      color: oklch(0.95 0 0);
+      -webkit-font-smoothing: antialiased;
+      -moz-osx-font-smoothing: grayscale;
+    }
+
+    .setup-card {
+      text-align: center;
+      max-width: 440px;
+      width: 100%;
+      padding: 48px 32px;
+      background: oklch(0.23 0.01 260);
+      border-radius: 12px;
+      border: 1px solid oklch(0.30 0.01 260);
+    }
+
+    h1 {
+      font-size: 2rem;
+      font-weight: 700;
+      margin-bottom: 8px;
+      color: oklch(0.91 0.19 102);
+    }
+
+    .subtitle {
+      font-size: 0.875rem;
+      color: oklch(0.65 0 0);
+      margin-bottom: 32px;
+    }
+
+    label {
+      display: block;
+      text-align: left;
+      font-size: 0.875rem;
+      font-weight: 500;
+      margin-bottom: 8px;
+      color: oklch(0.85 0 0);
+    }
+
+    input[type="url"] {
+      width: 100%;
+      padding: 12px 16px;
+      border-radius: 8px;
+      border: 1px solid oklch(0.30 0.01 260);
+      background: oklch(0.20 0.01 260);
+      color: oklch(0.95 0 0);
+      font-size: 1rem;
+      font-family: inherit;
+      outline: none;
+      transition: border-color 0.2s;
+    }
+
+    input[type="url"]:focus {
+      border-color: oklch(0.91 0.19 102);
+    }
+
+    input[type="url"]::placeholder {
+      color: oklch(0.45 0 0);
+    }
+
+    .error-message {
+      display: none;
+      text-align: left;
+      font-size: 0.8125rem;
+      color: oklch(0.55 0.2 27);
+      margin-top: 6px;
+    }
+
+    .warning-message {
+      display: none;
+      text-align: left;
+      font-size: 0.8125rem;
+      color: oklch(0.75 0.15 85);
+      margin-top: 6px;
+    }
+
+    button {
+      margin-top: 24px;
+      width: 100%;
+      padding: 12px 32px;
+      border-radius: 8px;
+      border: none;
+      background: oklch(0.91 0.19 102);
+      color: oklch(0.20 0.02 90);
+      cursor: pointer;
+      font-size: 1rem;
+      font-weight: 600;
+      font-family: inherit;
+      transition: opacity 0.2s;
+    }
+
+    button:hover {
+      opacity: 0.9;
+    }
+
+    button:active {
+      opacity: 0.8;
+    }
+
+    button:disabled {
+      opacity: 0.5;
+      cursor: not-allowed;
+    }
+  </style>
+</head>
+<body>
+  <div class="setup-card">
+    <h1>Tessera</h1>
+    <p class="subtitle">Desktop-Client einrichten</p>
+
+    <label for="server-url">Server-URL eingeben:</label>
+    <input
+      id="server-url"
+      type="url"
+      placeholder="https://tessera.example.com"
+      value="http://localhost:3000"
+      autocomplete="off"
+      spellcheck="false"
+    />
+    <p id="error-msg" class="error-message"></p>
+    <p id="warning-msg" class="warning-message"></p>
+
+    <button id="connect-btn" type="button">Verbinden</button>
+  </div>
+
+  <script type="module">
+    import { load } from '@tauri-apps/plugin-store';
+
+    const urlInput = document.getElementById('server-url');
+    const connectBtn = document.getElementById('connect-btn');
+    const errorMsg = document.getElementById('error-msg');
+    const warningMsg = document.getElementById('warning-msg');
+
+    /**
+     * Validate a server URL using the URL constructor.
+     * Returns { valid: boolean, warning: string | null, error: string | null }
+     */
+    function validateUrl(input) {
+      const trimmed = input.trim();
+
+      if (!trimmed) {
+        return { valid: false, warning: null, error: 'Bitte eine URL eingeben.' };
+      }
+
+      let parsed;
+      try {
+        parsed = new URL(trimmed);
+      } catch {
+        return { valid: false, warning: null, error: 'Ungueltige URL. Bitte eine gueltige URL eingeben (z.B. https://tessera.example.com).' };
+      }
+
+      // Only allow http and https protocols
+      if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
+        return { valid: false, warning: null, error: 'Nur HTTP und HTTPS URLs sind erlaubt.' };
+      }
+
+      // Warn on non-https for non-localhost addresses (T-06-01 mitigation)
+      const isLocalhost = parsed.hostname === 'localhost' || parsed.hostname === '127.0.0.1' || parsed.hostname === '::1';
+      if (parsed.protocol === 'http:' && !isLocalhost) {
+        return {
+          valid: true,
+          warning: 'Warnung: Unverschluesselte Verbindung (HTTP). Fuer Produktivumgebungen wird HTTPS empfohlen.',
+          error: null,
+        };
+      }
+
+      return { valid: true, warning: null, error: null };
+    }
+
+    function showError(message) {
+      errorMsg.textContent = message;
+      errorMsg.style.display = 'block';
+      warningMsg.style.display = 'none';
+    }
+
+    function showWarning(message) {
+      warningMsg.textContent = message;
+      warningMsg.style.display = 'block';
+      errorMsg.style.display = 'none';
+    }
+
+    function clearMessages() {
+      errorMsg.style.display = 'none';
+      warningMsg.style.display = 'none';
+    }
+
+    async function connect() {
+      clearMessages();
+
+      const rawUrl = urlInput.value;
+      const result = validateUrl(rawUrl);
+
+      if (!result.valid) {
+        showError(result.error);
+        return;
+      }
+
+      if (result.warning) {
+        showWarning(result.warning);
+      }
+
+      // Normalize the URL
+      const normalizedUrl = new URL(rawUrl.trim()).href;
+
+      // Disable button during save
+      connectBtn.disabled = true;
+      connectBtn.textContent = 'Verbinde...';
+
+      try {
+        const store = await load('config.json', { autoSave: true });
+        await store.set('server_url', normalizedUrl);
+
+        // Navigate the WebView to the configured server
+        window.location.href = normalizedUrl;
+      } catch (err) {
+        showError('Fehler beim Speichern der Konfiguration: ' + (err.message || err));
+        connectBtn.disabled = false;
+        connectBtn.textContent = 'Verbinden';
+      }
+    }
+
+    // Button click handler
+    connectBtn.addEventListener('click', connect);
+
+    // Enter key support
+    urlInput.addEventListener('keydown', (e) => {
+      if (e.key === 'Enter') {
+        connect();
+      }
+    });
+
+    // Clear error messages on input change
+    urlInput.addEventListener('input', clearMessages);
+  </script>
+</body>
+</html>