diff --git a/AGENTS.md b/AGENTS.md
index 032fef5..5e9a5ce 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -288,20 +288,37 @@ server.setRequestHandler(ListToolsRequestSchema, async () => ({
 
 ### Authentication Flow
 
-**Two Types of Auth**:
+**Three Types of Auth**:
 
 1. **Bearer Token** (AUTH_TOKEN):
    - Static token for Lambda authentication
    - Generated during deployment
    - Validates client requests to Lambda function
    - Stored in environment variable
+   - Required for `/mcp` JSON-RPC endpoint
 
-2. **OAuth Tokens** (Strava):
+2. **Authless Mode** (ALLOW_AUTHLESS):
+   - When `ALLOW_AUTHLESS=true` (default), SSE endpoints bypass auth
+   - Enables Claude.ai custom connectors (which don't support custom headers)
+   - Applies to: `/sse`, `/sse/`, `/message` endpoints
+   - Does NOT apply to: `/mcp` endpoint (still requires Bearer token)
+   - Security: Keep Lambda URL private when enabled
+
+3. **OAuth Tokens** (Strava):
    - Access token (short-lived, ~6 hours)
    - Refresh token (long-lived)
    - Automatically managed by StravaClient
    - Stored in environment variables (CLIENT_ID, CLIENT_SECRET, REFRESH_TOKEN)
 
+**Authentication Middleware Logic**:
+```typescript
+// Simplified auth flow
+if (path === '/health') → bypass auth
+if (ALLOW_AUTHLESS && (path === '/sse' || path === '/message')) → bypass auth
+if (path === '/message' && valid session) → bypass auth
+else → require Bearer token
+```
+
 ### Local Development Workflow
 
 ```bash
@@ -539,6 +556,7 @@ sam delete --stack-name strava-mcp-stack  # Delete deployment
 - `STRAVA_CLIENT_SECRET` - Strava API client secret
 - `STRAVA_REFRESH_TOKEN` - Strava OAuth refresh token
 - `AUTH_TOKEN` - Bearer token for Lambda authentication
+- `ALLOW_AUTHLESS` - When "true", SSE endpoints bypass auth (default: "true")
 - `NODE_ENV` - Environment (production/development)
 
 ### File Locations
diff --git a/README.md b/README.md
index a6f09dc..b3426b9 100644
--- a/README.md
+++ b/README.md
@@ -134,6 +134,32 @@ Need to see the config again? Run:
 bun run deploy:show-config
 ```
 
+### 5. Claude.ai Custom Connectors (Web/Mobile)
+
+Claude.ai custom connectors use **authless mode** via SSE transport. This is enabled by default (`ALLOW_AUTHLESS=true`).
+
+**Setup Steps:**
+1. Go to **Claude.ai** → **Settings** → **Connectors** → **Add custom connector**
+2. Enter just the **base URL** (no path): `https://your-function-url.lambda-url.us-east-1.on.aws`
+3. Claude.ai will automatically discover the `/sse` endpoint and connect
+4. Verify tools appear and can be invoked
+
+**Important Notes:**
+- Claude.ai does NOT support custom headers (no Bearer token auth)
+- Authless mode only applies to SSE endpoints (`/sse`, `/message`)
+- The `/mcp` JSON-RPC endpoint still requires Bearer token authentication
+- Keep your Lambda Function URL private for security
+
+**Security Considerations:**
+- Authless mode is **high risk** and should be treated as **personal-use-only**
+- If authless mode is enabled, anyone with your Lambda URL can access and act on your Strava data
+- Authless mode is **not recommended for production**; if you must use it, combine it with stricter controls such as AWS WAF IP allowlisting or an additional shared secret
+
+**Recommended secure deployment (authless disabled, Bearer tokens required everywhere):**
+```bash
+sam deploy --parameter-overrides AllowAuthless=false
+```
+
 ## Documentation
 
 📚 **[Full Documentation](https://stealinglight.github.io/StravaMCP)**
diff --git a/docs/authentication.md b/docs/authentication.md
index f57a3eb..bf6bf92 100644
--- a/docs/authentication.md
+++ b/docs/authentication.md
@@ -11,7 +11,13 @@ The Lambda function uses **Bearer token authentication** to secure access to you
 - ✅ Works with Claude web, mobile, and desktop
 - ✅ Easy to rotate tokens when needed
 
-## How It Works
+## Authentication Modes
+
+The server supports two authentication modes:
+
+### 1. Bearer Token Authentication (Default for `/mcp` endpoint)
+
+For Claude Desktop and other MCP clients that support custom headers.
 
 ```
 ┌──────────────┐
@@ -31,6 +37,33 @@ The Lambda function uses **Bearer token authentication** to secure access to you
 └──────────────┘
 ```
 
+### 2. Authless Mode (For Claude.ai Custom Connectors)
+
+Claude.ai custom connectors only support authless or OAuth 2.1 (DCR) connections. Since OAuth 2.1 with DCR is complex to implement, this server provides an **authless mode** for SSE endpoints.
+
+When `ALLOW_AUTHLESS=true` (default), the SSE transport endpoints (`/sse`, `/sse/`, `/message`) bypass authentication, allowing Claude.ai to connect without Bearer tokens.
+
+```
+┌──────────────┐
+│  Claude.ai   │
+│ (Web/Mobile) │
+└──────┬───────┘
+       │ SSE connection (no auth required)
+       ▼
+┌──────────────┐
+│   Lambda     │─── ALLOW_AUTHLESS=true
+│  (Middleware)│    Skips auth for SSE
+└──────┬───────┘
+       │ Direct access
+       ▼
+┌──────────────┐
+│  MCP Server  │
+│ (Strava API) │
+└──────────────┘
+```
+
+**Important**: The `/mcp` JSON-RPC endpoint still requires Bearer token authentication for backward compatibility with other clients.
+
 ## Setup Steps
 
 ### 1. Deploy and Auto-Generate AUTH_TOKEN
@@ -116,6 +149,20 @@ Add as a Custom Connector in Claude Settings:
 
 **Important**: The URL must end with `/mcp` - this is the MCP endpoint.
 
+#### Claude.ai Custom Connectors (Authless Mode)
+
+For Claude.ai web and mobile, use the authless SSE transport:
+
+1. Go to **Claude.ai** → **Settings** → **Connectors** → **Add custom connector**
+2. Enter just the **base URL** (no `/mcp` or `/sse` path):
+   ```
+   https://your-function-url.lambda-url.us-east-1.on.aws
+   ```
+3. Claude.ai will automatically discover the `/sse` endpoint
+4. Verify tools appear in the conversation
+
+**Note**: Authless mode is enabled by default (`ALLOW_AUTHLESS=true`). Claude.ai cannot send custom headers, so Bearer token auth is not supported for Claude.ai connectors.
+
 ### 4. Test Authentication
 
 Test that authentication is working:
@@ -171,6 +218,51 @@ To rotate your authentication token:
 - Use short or predictable tokens
 - Reuse tokens across multiple services
 
+## Authless Mode Configuration
+
+### Enabling Authless Mode (Default)
+
+Authless mode is **enabled by default** for Claude.ai compatibility. The `ALLOW_AUTHLESS` parameter is set to `"true"` in the SAM template.
+
+When enabled:
+- SSE endpoints (`/sse`, `/sse/`, `/message`) do not require authentication
+- The `/mcp` JSON-RPC endpoint still requires Bearer token authentication
+- Claude.ai custom connectors can connect using the base URL
+
+### Disabling Authless Mode
+
+To require Bearer token authentication for all endpoints:
+
+```bash
+# During deployment
+sam deploy --parameter-overrides AllowAuthless=false
+
+# Or update samconfig.toml
+[default.deploy.parameters]
+parameter_overrides = [
+  "AllowAuthless=false",
+  # ... other parameters
+]
+```
+
+When disabled:
+- All endpoints require Bearer token authentication
+- Claude.ai custom connectors will NOT work (they cannot send custom headers)
+- Only Claude Desktop and clients supporting custom headers can connect
+
+### Security Implications
+
+**Authless mode enabled (`ALLOW_AUTHLESS=true`, advanced / opt-in):**
+- ⚠️ Not enabled by default. Enabling this on a publicly accessible Lambda URL exposes `/sse`, `/sse/`, and `/message` without authentication.
+- ⚠️ Anyone who learns your Lambda URL (via logs, screenshots, or misconfiguration) can access your Strava-backed tools via SSE; URL secrecy alone is **not** sufficient protection.
+- ✅ Only enable for strictly local or personal use where you fully control access to the URL.
+- 💡 If you must use authless mode in a cloud environment, combine it with additional controls such as AWS WAF/IP allowlisting and/or an extra shared secret (e.g., a query parameter or header checked by your Lambda).
+
+**Authless mode disabled (`ALLOW_AUTHLESS=false`, recommended default):**
+- ✅ All requests require a valid Bearer token
+- ❌ Claude.ai custom connectors won't work
+- ✅ Maximum security for shared, team, or production environments
+
 ## Security Considerations
 
 ### What This Protects
diff --git a/src/config/env.ts b/src/config/env.ts
index 0cc7bab..a5d227f 100644
--- a/src/config/env.ts
+++ b/src/config/env.ts
@@ -12,6 +12,9 @@ const envSchema = z.object({
   STRAVA_REFRESH_TOKEN: z.string().min(1, 'STRAVA_REFRESH_TOKEN is required'),
   AUTH_TOKEN: z.string().min(32, 'AUTH_TOKEN must be at least 32 characters'),
   PORT: z.string().default('3000').transform(Number),
+  // ALLOW_AUTHLESS: When "true", bypasses auth for SSE endpoints (/sse, /sse/, /message)
+  // This enables Claude.ai custom connectors which don't support Bearer token auth
+  ALLOW_AUTHLESS: z.string().default('true').transform((val) => val.toLowerCase() === 'true'),
 });
 
 /**
@@ -25,6 +28,7 @@ export function getConfig() {
     STRAVA_REFRESH_TOKEN: process.env.STRAVA_REFRESH_TOKEN,
     AUTH_TOKEN: process.env.AUTH_TOKEN,
     PORT: process.env.PORT,
+    ALLOW_AUTHLESS: process.env.ALLOW_AUTHLESS,
   });
 
   if (!result.success) {
diff --git a/src/index.ts b/src/index.ts
index 16bf1f2..7d862ae 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -92,7 +92,7 @@ try {
 const server = new Server(
   {
     name: 'strava-mcp-server',
-    version: '1.0.0',
+    version: '3.0.0',
   },
   {
     capabilities: {
@@ -325,20 +325,27 @@ async function main() {
 
   // Authentication middleware for local dev (optional - can be disabled)
   // Supports both Authorization header and query parameter
+  // When ALLOW_AUTHLESS=true, SSE endpoints bypass auth for Claude.ai custom connectors
   app.use((req: Request, res: Response, next) => {
-    if (req.path === '/health') {
+    if (req.path === '/health' || req.path === '/debug') {
       return next();
     }
 
-    // For SSE endpoint, authentication happens via query param or header
-    if (req.path === '/sse' || req.path === '/sse/') {
-      // SSE authentication happens here before establishing connection
-      // Continue to token validation below
+    // Check if authless mode is enabled for SSE endpoints
+    // This allows Claude.ai custom connectors to connect without Bearer tokens
+    const isSSEEndpoint = req.path === '/sse' || req.path === '/sse/';
+    const isMessageEndpoint = req.path === '/message';
+
+    if (config.ALLOW_AUTHLESS && (isSSEEndpoint || isMessageEndpoint)) {
+      if (isSSEEndpoint) {
+        console.error('[StravaServer] Authless SSE connection allowed (ALLOW_AUTHLESS=true)');
+      }
+      return next();
     }
 
-    // For SSE message endpoint, trust valid session IDs
+    // For SSE message endpoint with valid session, trust the session
     const sessionId = req.query.sessionId as string;
-    if (req.path === '/message' && sessionId && transports[sessionId]) {
+    if (isMessageEndpoint && sessionId && transports[sessionId]) {
       return next();
     }
 
@@ -346,29 +353,63 @@ async function main() {
     // If AUTH_TOKEN is set in .env, validate it
     if (config.AUTH_TOKEN && config.AUTH_TOKEN.length > 0) {
       let token: string | undefined;
-      
+
       const authHeader = req.headers['authorization'];
       if (authHeader && authHeader.startsWith('Bearer ')) {
         token = authHeader.substring(7);
       } else if (req.query.token) {
         token = req.query.token as string;
       }
-      
+
       if (!token || token !== config.AUTH_TOKEN) {
         console.error('[StravaServer] Invalid or missing token');
-        return res.status(401).json({ 
+        return res.status(401).json({
           error: 'Unauthorized',
           message: 'Invalid or missing token'
         });
       }
     }
-    
+
     next();
   });
 
-  // Health check endpoint
+  // Health check endpoint - enhanced with diagnostic info
   app.get('/health', (_req: Request, res: Response) => {
-    res.json({ status: 'healthy', version: '2.0.0' });
+    res.json({
+      status: 'healthy',
+      version: '3.0.0',
+      runtime: 'local',
+      authless: config?.ALLOW_AUTHLESS ?? false,
+      timestamp: new Date().toISOString(),
+    });
+  });
+
+  // Debug endpoint - helps troubleshoot Claude.ai connection issues
+  app.get('/debug', (_req: Request, res: Response) => {
+    res.json({
+      status: 'ok',
+      version: '3.0.0',
+      authless_enabled: config?.ALLOW_AUTHLESS ?? false,
+      environment: process.env.NODE_ENV || 'development',
+      endpoints: {
+        health: '/health',
+        debug: '/debug',
+        sse: '/sse (GET, establishes SSE connection)',
+        message: '/message (POST, requires sessionId query param)',
+        mcp: '/mcp (POST, requires Bearer token)',
+      },
+      claude_ai_setup: {
+        connector_url: `Use base URL only: http://localhost:${config.PORT}`,
+        auth_mode: config?.ALLOW_AUTHLESS ? 'Authless (SSE endpoints bypass auth)' : 'Bearer token required',
+        transport: 'SSE',
+        note: 'For local testing with Claude.ai, use ngrok or similar to expose localhost',
+      },
+      sse_headers: {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache',
+        Connection: 'keep-alive',
+      },
+    });
   });
 
   // SSE endpoint - establishes the server-to-client event stream
@@ -453,7 +494,7 @@ async function main() {
             },
             serverInfo: {
               name: 'strava-mcp-server',
-              version: '2.0.0',
+              version: '3.0.0',
             },
           };
           break;
@@ -674,7 +715,10 @@ async function main() {
   app.listen(port, () => {
     console.error(`[StravaServer] Remote MCP server running on http://localhost:${port}`);
     console.error(`[StravaServer] MCP endpoint: http://localhost:${port}/mcp`);
+    console.error(`[StravaServer] SSE endpoint: http://localhost:${port}/sse`);
     console.error(`[StravaServer] Health check: http://localhost:${port}/health`);
+    console.error(`[StravaServer] Debug info: http://localhost:${port}/debug`);
+    console.error(`[StravaServer] Authless mode: ${config.ALLOW_AUTHLESS ? 'ENABLED' : 'DISABLED'}`);
   });
 }
 
diff --git a/src/lambda.ts b/src/lambda.ts
index faf4a88..0f6f4b0 100644
--- a/src/lambda.ts
+++ b/src/lambda.ts
@@ -73,6 +73,19 @@ import {
  *
  * Wraps the Express-based MCP server for AWS Lambda using serverless-express.
  * Implements JSON-RPC over HTTP transport for Claude connector compatibility.
+ *
+ * SSE STREAMING NOTE:
+ * The @codegenie/serverless-express library does NOT support Lambda response streaming
+ * (see https://github.com/CodeGenieApp/serverless-express/issues/655).
+ * While the Lambda Function URL is configured with InvokeMode: RESPONSE_STREAM,
+ * the serverless-express wrapper buffers responses before sending.
+ *
+ * CURRENT WORKAROUND: The /mcp JSON-RPC endpoint works reliably for all clients.
+ * Claude.ai should connect to the base URL and use SSE, but if SSE doesn't work,
+ * alternative approaches include:
+ * 1. AWS Lambda Web Adapter (https://github.com/awslabs/aws-lambda-web-adapter)
+ * 2. Direct Lambda streaming without Express wrapper for SSE endpoints
+ * 3. Using awslambda.streamifyResponse() for native streaming support
  */
 
 // Initialize configuration
@@ -89,27 +102,39 @@ function initializeServer(): express.Application {
   const transports: Record<string, SSEServerTransport> = {};
 
   // Authentication middleware - verify Bearer token
-  // Skip auth for health check endpoint
+  // Skip auth for health check and debug endpoints
   // Supports both Authorization header and query parameter for Claude connector compatibility
+  // When ALLOW_AUTHLESS=true, SSE endpoints bypass auth for Claude.ai custom connectors
   app.use((req: Request, res: Response, next) => {
-    if (req.path === '/health') {
+    if (req.path === '/health' || req.path === '/debug') {
       return next();
     }
 
-    // For SSE endpoint, authentication happens via query param or header
-    if (req.path === '/sse' || req.path === '/sse/') {
-      // SSE authentication happens here before establishing connection
-      // Continue to token validation below
+    if (!config) {
+      // Initialize config if not already done (shouldn't happen, but safety check)
+      config = getConfig();
+    }
+
+    // Check if authless mode is enabled for SSE endpoints
+    // This allows Claude.ai custom connectors to connect without Bearer tokens
+    const isSSEEndpoint = req.path === '/sse' || req.path === '/sse/';
+    const isMessageEndpoint = req.path === '/message';
+
+    if (config.ALLOW_AUTHLESS && (isSSEEndpoint || isMessageEndpoint)) {
+      if (isSSEEndpoint) {
+        console.error('[StravaLambda] Authless SSE connection allowed (ALLOW_AUTHLESS=true)');
+      }
+      return next();
     }
 
-    // For SSE message endpoint, trust valid session IDs
+    // For SSE message endpoint with valid session, trust the session
     const sessionId = req.query.sessionId as string;
-    if (req.path === '/message' && sessionId && transports[sessionId]) {
+    if (isMessageEndpoint && sessionId && transports[sessionId]) {
       return next();
     }
 
     let token: string | undefined;
-    
+
     // Try Authorization header first (preferred for API clients)
     const authHeader = req.headers['authorization'];
     if (authHeader && authHeader.startsWith('Bearer ')) {
@@ -119,15 +144,10 @@ function initializeServer(): express.Application {
     else if (req.query.token) {
       token = req.query.token as string;
     }
-    
-    if (!config) {
-      // Initialize config if not already done (shouldn't happen, but safety check)
-      config = getConfig();
-    }
 
     if (!token || token !== config.AUTH_TOKEN) {
       console.error('[StravaLambda] Invalid or missing token');
-      return res.status(401).json({ 
+      return res.status(401).json({
         error: 'Unauthorized',
         message: 'Invalid or missing token. Use: Authorization: Bearer <token> OR ?token=<token>'
       });
@@ -154,7 +174,7 @@ function initializeServer(): express.Application {
   mcpServer = new Server(
     {
       name: 'strava-mcp-server',
-      version: '2.0.0',
+      version: '3.0.0',
     },
     {
       capabilities: {
@@ -377,9 +397,48 @@ function initializeServer(): express.Application {
     }
   });
 
-  // Health check endpoint
+  // Health check endpoint - enhanced with diagnostic info
   app.get('/health', (_req: Request, res: Response) => {
-    res.json({ status: 'healthy', version: '2.0.0', environment: 'lambda' });
+    res.json({
+      status: 'healthy',
+      version: '3.0.0',
+      runtime: 'lambda',
+      authless: config?.ALLOW_AUTHLESS ?? false,
+      timestamp: new Date().toISOString(),
+    });
+  });
+
+  // Debug endpoint - helps troubleshoot Claude.ai connection issues
+  app.get('/debug', (_req: Request, res: Response) => {
+    res.json({
+      status: 'ok',
+      version: '3.0.0',
+      authless_enabled: config?.ALLOW_AUTHLESS ?? false,
+      environment: process.env.NODE_ENV || 'development',
+      endpoints: {
+        health: '/health',
+        debug: '/debug',
+        sse: '/sse (GET, establishes SSE connection)',
+        message: '/message (POST, requires sessionId query param)',
+        mcp: '/mcp (POST, requires Bearer token)',
+      },
+      claude_ai_setup: {
+        connector_url: 'Use base URL only, no path (e.g., https://xyz.lambda-url.us-east-1.on.aws)',
+        auth_mode: config?.ALLOW_AUTHLESS ? 'Authless (SSE endpoints bypass auth)' : 'Bearer token required',
+        transport: 'SSE',
+        note: 'Claude.ai will auto-discover /sse endpoint from base URL',
+      },
+      sse_headers: {
+        'Content-Type': 'text/event-stream',
+        'Cache-Control': 'no-cache',
+        Connection: 'keep-alive',
+      },
+      known_limitations: {
+        sse_streaming: 'serverless-express does not support Lambda response streaming (see GitHub issue #655)',
+        workaround: 'If SSE fails, consider AWS Lambda Web Adapter or direct Lambda streaming',
+        mcp_endpoint: '/mcp JSON-RPC endpoint works reliably for all clients',
+      },
+    });
   });
 
   // SSE endpoint - establishes the server-to-client event stream
@@ -464,7 +523,7 @@ function initializeServer(): express.Application {
             },
             serverInfo: {
               name: 'strava-mcp-server',
-              version: '2.0.0',
+              version: '3.0.0',
             },
           };
           break;
diff --git a/template.yaml b/template.yaml
index e944fb6..fc3a0b2 100644
--- a/template.yaml
+++ b/template.yaml
@@ -8,7 +8,7 @@ Description: >
 
 Globals:
   Function:
-    Timeout: 300  # 5 minutes (Lambda max for Function URLs)
+    Timeout: 900  # 15 minutes (max for Lambda Function URLs) - needed for long SSE connections
     MemorySize: 512  # MB (Free tier allows up to 3.2M seconds of 512MB compute)
     Runtime: nodejs20.x
     Architectures:
@@ -39,6 +39,14 @@ Parameters:
     NoEcho: true
     MinLength: 32
 
+  AllowAuthless:
+    Type: String
+    Description: When "true", allows SSE connections without authentication (for Claude.ai custom connectors)
+    Default: "true"
+    AllowedValues:
+      - "true"
+      - "false"
+
 Resources:
   StravaMCPFunction:
     Type: AWS::Serverless::Function
@@ -53,15 +61,23 @@ Resources:
           STRAVA_CLIENT_SECRET: !Ref StravaClientSecret
           STRAVA_REFRESH_TOKEN: !Ref StravaRefreshToken
           AUTH_TOKEN: !Ref AuthToken
+          ALLOW_AUTHLESS: !Ref AllowAuthless
       FunctionUrlConfig:
         AuthType: NONE  # Public URL with Bearer token authentication in application code
         Cors:
           AllowOrigins:
-            - '*'
+            - '*'  # Allow all origins for flexibility (Claude.ai, Claude Desktop, etc.)
           AllowMethods:
-            - '*'
+            - GET
+            - POST
+            - OPTIONS
           AllowHeaders:
-            - '*'
+            - Content-Type
+            - Authorization
+            - Accept
+            - X-Requested-With
+          AllowCredentials: false
+          MaxAge: 86400  # Cache preflight for 24 hours
         InvokeMode: RESPONSE_STREAM  # Enable streaming for SSE support
       Tags:
         Project: StravaMCP