fix: add required Accept header for streamable HTTP transport

When connecting to MCP servers via streamable HTTP, mcptools was not
setting the Accept header. Some servers like mcp.grep.app require
clients to accept both application/json and text/event-stream, and
return 405 errors when this header is missing.

This change ensures the Accept header is always set for both HTTP
and SSE transports, fixing compatibility with servers that enforce
this requirement.

Tested with mcp.grep.app and existing unit tests pass.

Author: ethan-huo

cmd/mcptools/commands/utils.go

@@ -116,26 +116,24 @@ var CreateClientFunc = func(args []string, _ ...client.ClientOption) (*client.Cl
 			return nil, fmt.Errorf("failed to parse authentication: %w", authErr)
 		}
 
-		// Create headers map if authentication is provided
+		// Create headers map with required Accept header for MCP protocol
 		headers := make(map[string]string)
+
+		// Add authentication header if provided
 		if authHeader != "" {
 			headers["Authorization"] = authHeader
 		}
 
+		// Add Accept header required by MCP streamable HTTP and SSE transports
+		// Many MCP servers require clients to accept both JSON responses and event streams
+		headers["Accept"] = "application/json, text/event-stream"
+
 		if TransportOption == "sse" {
 			// For SSE transport, use transport.ClientOption
-			if len(headers) > 0 {
-				c, err = client.NewSSEMCPClient(cleanURL, transport.WithHeaders(headers))
-			} else {
-				c, err = client.NewSSEMCPClient(cleanURL)
-			}
+			c, err = client.NewSSEMCPClient(cleanURL, transport.WithHeaders(headers))
 		} else {
 			// For StreamableHTTP transport, use transport.StreamableHTTPCOption
-			if len(headers) > 0 {
-				c, err = client.NewStreamableHttpClient(cleanURL, transport.WithHTTPHeaders(headers))
-			} else {
-				c, err = client.NewStreamableHttpClient(cleanURL)
-			}
+			c, err = client.NewStreamableHttpClient(cleanURL, transport.WithHTTPHeaders(headers))
 		}
 
 		if err != nil {