diff --git a/src/cliproxy/auth/auth-types.ts b/src/cliproxy/auth/auth-types.ts
index 234a00ba..1f66114f 100644
--- a/src/cliproxy/auth/auth-types.ts
+++ b/src/cliproxy/auth/auth-types.ts
@@ -15,19 +15,19 @@ import { AccountInfo } from '../account-manager';
  * - Gemini: Authorization Code Flow with local callback server on port 8085
  * - Codex:  Authorization Code Flow with local callback server on port 1455
  * - Agy:    Authorization Code Flow with local callback server on port 51121
- * - Kiro:   Authorization Code Flow with local callback server on port 9876
  * - iFlow:  Authorization Code Flow with local callback server on port 11451
  * - Claude: Authorization Code Flow with local callback server on port 54545 (Anthropic OAuth)
+ * - Kiro:   Device Code Flow (polling-based, NO callback port needed)
  * - Qwen:   Device Code Flow (polling-based, NO callback port needed)
  * - GHCP:   Device Code Flow (polling-based, NO callback port needed)
  */
 export const OAUTH_CALLBACK_PORTS: Partial<Record<CLIProxyProvider, number>> = {
   gemini: 8085,
-  kiro: 9876,
   codex: 1455,
   agy: 51121,
   iflow: 11451,
   claude: 54545,
+  // kiro: Device Code Flow - no callback port
   // qwen: Device Code Flow - no callback port
   // ghcp: Device Code Flow - no callback port
 };
diff --git a/src/management/oauth-port-diagnostics.ts b/src/management/oauth-port-diagnostics.ts
index d50c16cf..8a13628d 100644
--- a/src/management/oauth-port-diagnostics.ts
+++ b/src/management/oauth-port-diagnostics.ts
@@ -9,7 +9,7 @@
  * - Codex: 1455
  * - Agy: 51121
  * - iFlow: 11451
- * - Kiro: 9876
+ * - Kiro: Device Code Flow (no port needed)
  * - Claude: 54545
  * - Qwen: Device Code Flow (no port needed)
  * - GHCP: Device Code Flow (no port needed)
@@ -26,40 +26,44 @@ import {
 } from '../utils/port-utils';
 import { CLIProxyProvider } from '../cliproxy/types';
 import { CLIPROXY_PROFILES } from '../auth/profile-detector';
+import {
+  CLIPROXY_PROVIDER_IDS,
+  getOAuthCallbackPort,
+  getOAuthFlowType,
+  type OAuthFlowType as ProviderOAuthFlowType,
+} from '../cliproxy/provider-capabilities';
 
 /**
- * OAuth callback ports for each provider
- * Extracted from CLIProxyAPI source
+ * Build provider-indexed records from canonical provider capabilities.
+ * Keeps diagnostics in sync with runtime OAuth flow metadata.
  */
-export const OAUTH_CALLBACK_PORTS: Record<CLIProxyProvider, number | null> = {
-  gemini: 8085,
-  codex: 1455,
-  agy: 51121,
-  qwen: null, // Device Code Flow - no callback port
-  iflow: 11451, // Authorization Code Flow
-  kiro: 9876, // Authorization Code Flow
-  ghcp: null, // Device Code Flow - no callback port
-  claude: 54545, // Authorization Code Flow (Anthropic OAuth)
-};
+function buildProviderMap<T>(
+  valueFor: (provider: CLIProxyProvider) => T
+): Record<CLIProxyProvider, T> {
+  return CLIPROXY_PROVIDER_IDS.reduce(
+    (acc, provider) => {
+      acc[provider] = valueFor(provider);
+      return acc;
+    },
+    {} as Record<CLIProxyProvider, T>
+  );
+}
+
+export const OAUTH_CALLBACK_PORTS: Record<CLIProxyProvider, number | null> = buildProviderMap(
+  (provider) => getOAuthCallbackPort(provider)
+);
 
 /**
  * OAuth flow types
  */
-export type OAuthFlowType = 'authorization_code' | 'device_code';
+export type OAuthFlowType = ProviderOAuthFlowType;
 
 /**
  * OAuth flow type per provider
  */
-export const OAUTH_FLOW_TYPES: Record<CLIProxyProvider, OAuthFlowType> = {
-  gemini: 'authorization_code',
-  codex: 'authorization_code',
-  agy: 'authorization_code',
-  qwen: 'device_code',
-  iflow: 'authorization_code',
-  kiro: 'authorization_code',
-  ghcp: 'device_code',
-  claude: 'authorization_code',
-};
+export const OAUTH_FLOW_TYPES: Record<CLIProxyProvider, OAuthFlowType> = buildProviderMap(
+  (provider) => getOAuthFlowType(provider)
+);
 
 /**
  * Port diagnostic result
diff --git a/src/web-server/routes/cliproxy-auth-routes.ts b/src/web-server/routes/cliproxy-auth-routes.ts
index 302323ba..0930e873 100644
--- a/src/web-server/routes/cliproxy-auth-routes.ts
+++ b/src/web-server/routes/cliproxy-auth-routes.ts
@@ -38,6 +38,7 @@ import {
   CLIPROXY_CALLBACK_PROVIDER_MAP,
   CLIPROXY_AUTH_URL_PROVIDER_MAP,
 } from '../../cliproxy/auth/auth-types';
+import { getOAuthFlowType } from '../../cliproxy/provider-capabilities';
 import type { CLIProxyProvider } from '../../cliproxy/types';
 import { CLIPROXY_PROFILES } from '../../auth/profile-detector';
 
@@ -46,6 +47,13 @@ const router = Router();
 // Valid providers list - derived from canonical CLIPROXY_PROFILES
 const validProviders: CLIProxyProvider[] = [...CLIPROXY_PROFILES];
 
+export function getStartUrlUnsupportedReason(provider: CLIProxyProvider): string | null {
+  if (getOAuthFlowType(provider) === 'device_code') {
+    return `Provider '${provider}' uses Device Code flow. Use /api/cliproxy/auth/${provider}/start instead.`;
+  }
+  return null;
+}
+
 /**
  * GET /api/cliproxy/auth - Get auth status for built-in CLIProxy profiles
  * Also fetches CLIProxyAPI stats to update lastUsedAt for active providers
@@ -557,6 +565,11 @@ router.post('/:provider/start-url', async (req: Request, res: Response): Promise
     res.status(400).json({ error: `Invalid provider: ${provider}` });
     return;
   }
+  const unsupportedReason = getStartUrlUnsupportedReason(provider as CLIProxyProvider);
+  if (unsupportedReason) {
+    res.status(400).json({ error: unsupportedReason });
+    return;
+  }
 
   try {
     const authUrlProvider =
diff --git a/tests/unit/cliproxy/provider-capabilities.test.ts b/tests/unit/cliproxy/provider-capabilities.test.ts
index 7aa13e7e..3434c344 100644
--- a/tests/unit/cliproxy/provider-capabilities.test.ts
+++ b/tests/unit/cliproxy/provider-capabilities.test.ts
@@ -2,11 +2,17 @@ import { describe, expect, it } from 'bun:test';
 import {
   CLIPROXY_PROVIDER_IDS,
   getOAuthCallbackPort,
+  getOAuthFlowType,
   getProviderDisplayName,
   getProvidersByOAuthFlow,
   isCLIProxyProvider,
   mapExternalProviderName,
 } from '../../../src/cliproxy/provider-capabilities';
+import {
+  OAUTH_CALLBACK_PORTS as DIAGNOSTIC_CALLBACK_PORTS,
+  OAUTH_FLOW_TYPES,
+} from '../../../src/management/oauth-port-diagnostics';
+import { OAUTH_CALLBACK_PORTS as AUTH_CALLBACK_PORTS } from '../../../src/cliproxy/auth/auth-types';
 
 describe('provider-capabilities', () => {
   it('keeps canonical provider IDs backward-compatible', () => {
@@ -56,4 +62,17 @@ describe('provider-capabilities', () => {
     expect(getOAuthCallbackPort('gemini')).toBe(8085);
     expect(getProviderDisplayName('agy')).toBe('AntiGravity');
   });
+
+  it('keeps diagnostics flow metadata in sync with provider capabilities', () => {
+    for (const provider of CLIPROXY_PROVIDER_IDS) {
+      expect(OAUTH_FLOW_TYPES[provider]).toBe(getOAuthFlowType(provider));
+      expect(DIAGNOSTIC_CALLBACK_PORTS[provider]).toBe(getOAuthCallbackPort(provider));
+    }
+  });
+
+  it('does not define callback ports for device code providers in auth constants', () => {
+    for (const provider of getProvidersByOAuthFlow('device_code')) {
+      expect(AUTH_CALLBACK_PORTS[provider]).toBeUndefined();
+    }
+  });
 });
diff --git a/tests/unit/web-server/cliproxy-auth-routes.test.ts b/tests/unit/web-server/cliproxy-auth-routes.test.ts
new file mode 100644
index 00000000..025c0e8b
--- /dev/null
+++ b/tests/unit/web-server/cliproxy-auth-routes.test.ts
@@ -0,0 +1,16 @@
+import { describe, expect, it } from 'bun:test';
+import { getStartUrlUnsupportedReason } from '../../../src/web-server/routes/cliproxy-auth-routes';
+
+describe('cliproxy-auth-routes start-url guard', () => {
+  it('rejects device code providers', () => {
+    expect(getStartUrlUnsupportedReason('kiro')).toContain("Provider 'kiro' uses Device Code flow");
+    expect(getStartUrlUnsupportedReason('ghcp')).toContain("Provider 'ghcp' uses Device Code flow");
+    expect(getStartUrlUnsupportedReason('qwen')).toContain("Provider 'qwen' uses Device Code flow");
+  });
+
+  it('allows authorization code providers', () => {
+    expect(getStartUrlUnsupportedReason('gemini')).toBeNull();
+    expect(getStartUrlUnsupportedReason('codex')).toBeNull();
+    expect(getStartUrlUnsupportedReason('claude')).toBeNull();
+  });
+});
diff --git a/ui/src/components/account/add-account-dialog.tsx b/ui/src/components/account/add-account-dialog.tsx
index 55ef8079..abae2ba8 100644
--- a/ui/src/components/account/add-account-dialog.tsx
+++ b/ui/src/components/account/add-account-dialog.tsx
@@ -1,7 +1,7 @@
 /**
  * Add Account Dialog Component
  * Uses /start-url to get OAuth URL + polls for completion via management API.
- * For Device Code flows (ghcp, qwen): Uses /start endpoint which spawns CLIProxy
+ * For Device Code flows (ghcp, qwen, kiro): Uses /start endpoint which spawns CLIProxy
  * binary and emits WebSocket events. DeviceCodeDialog handles user code display.
  * Shows auth URL + callback paste field. Polling auto-closes on success.
  * For Kiro: Also shows "Import from IDE" option.
@@ -22,7 +22,7 @@ import { Loader2, ExternalLink, User, Download, Copy, Check } from 'lucide-react
 import { useKiroImport } from '@/hooks/use-cliproxy';
 import { useCliproxyAuthFlow } from '@/hooks/use-cliproxy-auth-flow';
 import { applyDefaultPreset } from '@/lib/preset-utils';
-import { isDeviceCodeProvider } from '@/lib/provider-config';
+import { isDeviceCodeProvider, isNicknameRequiredProvider } from '@/lib/provider-config';
 import { toast } from 'sonner';
 
 interface AddAccountDialogProps {
@@ -44,18 +44,23 @@ export function AddAccountDialog({
   const [nickname, setNickname] = useState('');
   const [callbackUrl, setCallbackUrl] = useState('');
   const [copied, setCopied] = useState(false);
+  const [localError, setLocalError] = useState<string | null>(null);
   const wasAuthenticatingRef = useRef(false);
   const authFlow = useCliproxyAuthFlow();
   const kiroImportMutation = useKiroImport();
 
   const isKiro = provider === 'kiro';
   const isDeviceCode = isDeviceCodeProvider(provider);
+  const requiresNickname = isNicknameRequiredProvider(provider);
   const isPending = authFlow.isAuthenticating || kiroImportMutation.isPending;
+  const nicknameTrimmed = nickname.trim();
+  const errorMessage = localError || authFlow.error;
 
   const resetAndClose = () => {
     setNickname('');
     setCallbackUrl('');
     setCopied(false);
+    setLocalError(null);
     wasAuthenticatingRef.current = false;
     onClose();
   };
@@ -103,13 +108,18 @@ export function AddAccountDialog({
   };
 
   /**
-   * Authenticate via /start-url + polling only.
-   * Does NOT call /start (which spawns a local CLIProxy binary that kills running instances).
-   * /start-url uses the management API to get auth URL, then polls for completion.
+   * Start auth flow using provider capabilities.
+   * - Device code providers use /start and rely on WebSocket events for code display.
+   * - Authorization code providers use /start-url and polling.
    */
   const handleAuthenticate = () => {
+    if (requiresNickname && !nicknameTrimmed) {
+      setLocalError(`Nickname is required for ${displayName} accounts.`);
+      return;
+    }
+    setLocalError(null);
     wasAuthenticatingRef.current = true;
-    authFlow.startAuth(provider, { nickname: nickname.trim() || undefined });
+    authFlow.startAuth(provider, { nickname: nicknameTrimmed || undefined });
   };
 
   const handleKiroImport = () => {
@@ -157,20 +167,27 @@ export function AddAccountDialog({
           {/* Nickname input - only show before auth starts */}
           {!showAuthUI && (
             <div className="space-y-2">
-              <Label htmlFor="nickname">Nickname (optional)</Label>
+              <Label htmlFor="nickname">
+                {requiresNickname ? 'Nickname (required)' : 'Nickname (optional)'}
+              </Label>
               <div className="flex items-center gap-2">
                 <User className="w-4 h-4 text-muted-foreground" />
                 <Input
                   id="nickname"
                   value={nickname}
-                  onChange={(e) => setNickname(e.target.value)}
+                  onChange={(e) => {
+                    setNickname(e.target.value);
+                    setLocalError(null);
+                  }}
                   placeholder="e.g., work, personal"
                   disabled={isPending}
                   className="flex-1"
                 />
               </div>
               <p className="text-xs text-muted-foreground">
-                A friendly name to identify this account. Auto-generated from email if left empty.
+                {requiresNickname
+                  ? 'Required for this provider. Use a unique friendly name (e.g., work, personal).'
+                  : 'A friendly name to identify this account. Auto-generated from email if left empty.'}
               </p>
             </div>
           )}
@@ -191,11 +208,6 @@ export function AddAccountDialog({
                 </p>
               </div>
 
-              {/* Error display */}
-              {authFlow.error && !authFlow.authUrl && (
-                <p className="text-xs text-center text-destructive">{authFlow.error}</p>
-              )}
-
               {/* Auth URL section - only for Authorization Code flows, NOT Device Code */}
               {authFlow.authUrl && !authFlow.isDeviceCodeFlow && (
                 <div className="space-y-3">
@@ -273,6 +285,9 @@ export function AddAccountDialog({
             </div>
           )}
 
+          {/* Persist error visibility outside auth-only UI states */}
+          {errorMessage && <p className="text-xs text-center text-destructive">{errorMessage}</p>}
+
           {/* Kiro import loading */}
           {kiroImportMutation.isPending && (
             <p className="text-sm text-center text-muted-foreground">
@@ -302,7 +317,10 @@ export function AddAccountDialog({
               </Button>
             )}
             {!showAuthUI && (
-              <Button onClick={handleAuthenticate} disabled={isPending}>
+              <Button
+                onClick={handleAuthenticate}
+                disabled={isPending || (requiresNickname && !nicknameTrimmed)}
+              >
                 <ExternalLink className="w-4 h-4 mr-2" />
                 Authenticate
               </Button>
diff --git a/ui/src/hooks/use-cliproxy-auth-flow.ts b/ui/src/hooks/use-cliproxy-auth-flow.ts
index 433af6e2..73a1d5c4 100644
--- a/ui/src/hooks/use-cliproxy-auth-flow.ts
+++ b/ui/src/hooks/use-cliproxy-auth-flow.ts
@@ -19,7 +19,7 @@ interface AuthFlowState {
   oauthState: string | null;
   /** Whether callback is being submitted */
   isSubmittingCallback: boolean;
-  /** Whether this is a device code flow (ghcp, qwen) - dialog handled separately via WebSocket */
+  /** Whether this is a device code flow (ghcp, qwen, kiro) - dialog handled separately via WebSocket */
   isDeviceCodeFlow: boolean;
 }
 
diff --git a/ui/src/hooks/use-device-code.ts b/ui/src/hooks/use-device-code.ts
index a8492068..8c69bd77 100644
--- a/ui/src/hooks/use-device-code.ts
+++ b/ui/src/hooks/use-device-code.ts
@@ -3,7 +3,7 @@
  *
  * Listens for WebSocket device code events and manages dialog state.
  * Similar to useProjectSelection but for Device Code OAuth flows
- * (GitHub Copilot, Qwen, etc.)
+ * (GitHub Copilot, Qwen, Kiro, etc.)
  */
 
 import { useState, useEffect, useCallback, useMemo } from 'react';
@@ -26,6 +26,7 @@ interface DeviceCodeState {
 /** Provider display names for user-friendly messages */
 const PROVIDER_DISPLAY_NAMES: Record<string, string> = {
   ghcp: 'GitHub Copilot',
+  kiro: 'Kiro (AWS)',
   qwen: 'Qwen Code',
 };
 
diff --git a/ui/src/lib/provider-config.ts b/ui/src/lib/provider-config.ts
index bdcbd378..2da393ba 100644
--- a/ui/src/lib/provider-config.ts
+++ b/ui/src/lib/provider-config.ts
@@ -82,3 +82,11 @@ export const DEVICE_CODE_PROVIDERS: CLIProxyProvider[] = ['ghcp', 'kiro', 'qwen'
 export function isDeviceCodeProvider(provider: string): boolean {
   return DEVICE_CODE_PROVIDERS.includes(provider as CLIProxyProvider);
 }
+
+/** Providers that require nickname because token payload may not include email. */
+export const NICKNAME_REQUIRED_PROVIDERS: CLIProxyProvider[] = ['ghcp', 'kiro'];
+
+/** Check if provider requires user-supplied nickname in auth flow */
+export function isNicknameRequiredProvider(provider: string): boolean {
+  return NICKNAME_REQUIRED_PROVIDERS.includes(provider as CLIProxyProvider);
+}