feat: add flag to enable draft specs

cmd/internal/flags.go

@@ -72,4 +72,5 @@ func ServeFlags(flags *pflag.FlagSet, opts *ToolboxOptions) {
 	flags.StringVar(&opts.Cfg.McpPrmFile, "mcp-prm-file", "", "Path to a manual Protected Resource Metadata (PRM) JSON file. If provided, overrides auto-generation.")
 	flags.StringSliceVar(&opts.Cfg.AllowedOrigins, "allowed-origins", []string{"*"}, "Specifies a list of origins permitted to access this server. Defaults to '*'.")
 	flags.StringSliceVar(&opts.Cfg.AllowedHosts, "allowed-hosts", []string{"*"}, "Specifies a list of hosts permitted to access this server. Defaults to '*'.")
+	flags.BoolVar(&opts.Cfg.EnableDraftSpecs, "enable-draft-specs", false, "Opt-in and test upcoming draft MCP specifications.")
 }

docs/en/documentation/introduction/_index.md

@@ -762,3 +762,42 @@ For more detailed instructions on using the Toolbox Go SDK, see the
 [README](https://github.com/googleapis/mcp-toolbox-sdk-go/blob/main/core/README.md).
 
 For more details, see the [Agent Skills guide](https://mcp-toolbox.dev/documentation/configuration/skills/).
+
+## Supported MCP Version
+
+Toolbox is fully compatible with the Model Context Protocol (MCP) and maintains support for multiple protocol revisions to ensure seamless integration with most MCP clients.
+
+### Stable Releases
+The following official MCP specification versions are currently supported for production use:
+
+* `2025-11-25`
+* `2025-06-18`
+* `2025-03-26`
+* `2024-11-05`
+
+{{< notice note >}}
+If no protocol version is negotiated or provided, the Toolbox server defaults to
+the legacy custom transport protocol established on `2024-11-05`, which does not
+require initialization.
+{{< /notice >}}
+
+### Draft Specifications
+We actively develop against upcoming protocol specifications. You can opt-in to
+test these forthcoming revisions before their official release using the
+`--enable-draft-specs` flag during server startup.
+
+To test these draft specifications, enable the startup flag and use this version
+string during negotiation:
+* `DRAFT-2026-v1`
+
+Description: Enables experimental support for upcoming draft MCP specifications,
+allowing you to test new schema standards and transport adjustments before they
+become stable.
+
+{{< notice note >}}
+Once the draft specification is finalized and released as a stable version, the
+draft implementation will be permanently removed. There will be no automatic
+redirects or backwards compatibility from the draft spec to the stable release.
+Developers must manually migrate their clients to the stable version once it is
+available. Do not use this flag in production environments.
+{{< /notice >}}

docs/en/reference/cli.md

@@ -13,7 +13,7 @@ description: >
 | `-a`         | `--address`                | Address of the interface the server will listen on.                                                                                                                       | `127.0.0.1` |
 |              | `--disable-reload`         | Disables dynamic reloading config.                                                                                                                                        |             |
 | `-h`         | `--help`                   | help for toolbox                                                                                                                                                          |             |
-|              | `--ignore-unknown-tools`   | Log warnings and skip unknown/unsupported tool types instead of failing to start.                                                                                          |             |
+|              | `--ignore-unknown-tools`   | Log warnings and skip unknown/unsupported tool types instead of failing to start.                                                                                         |             |
 |              | `--log-level`              | Specify the minimum level logged. Allowed: 'DEBUG', 'INFO', 'WARN', 'ERROR'.                                                                                              | `info`      |
 |              | `--logging-format`         | Specify logging format to use. Allowed: 'standard' or 'JSON'.                                                                                                             | `standard`  |
 |              | `--mcp-prm-file`           | Path to a manual Protected Resource Metadata (PRM) JSON file. If provided, overrides auto-generation for MCP Server-Wide Authentication.                                  |             |
@@ -35,6 +35,7 @@ description: >
 |              | `--allowed-hosts`          | Specifies a list of hosts permitted to access this server to prevent DNS rebinding attacks.                                                                               | `*`         |
 |              | `--user-agent-metadata`    | Appends additional metadata to the User-Agent.                                                                                                                            |             |
 |              | `--poll-interval`          | Specifies the polling frequency (seconds) for configuration file updates.                                                                                                 | `0`         |
+|              | `--enable-draft-specs`     | Opt-in and test upcoming draft MCP specifications.                                                                                                                        | `false`     |
 | `-v`         | `--version`                | version for toolbox                                                                                                                                                       |             |
 
 ## Sub Commands

internal/server/config.go

@@ -95,6 +95,8 @@ type ServerConfig struct {
 	UserAgentMetadata []string
 	// PollInterval sets the polling frequency for configuration file updates.
 	PollInterval int
+	// EnableDraftSpecs allow users to opt-in and test upcoming draft MCP specs.
+	EnableDraftSpecs bool
 }
 
 type logFormat string

internal/server/mcp.go

@@ -813,7 +813,7 @@ func processMcpMessage(ctx context.Context, body []byte, s *Server, protocolVers
 			version = mcputil.LATEST_PROTOCOL_VERSION
 		}
 
-		result, err := mcp.ProcessMethod(ctx, version, baseMessage.Id, baseMessage.Method, tools.Toolset{}, prompts.Promptset{}, nil, body, nil)
+		result, err := mcp.ProcessMethod(ctx, s.enableDraftSpecs, version, baseMessage.Id, baseMessage.Method, tools.Toolset{}, prompts.Promptset{}, nil, body, nil)
 		if err != nil {
 			span.SetStatus(codes.Error, err.Error())
 			if rpcErr, ok := result.(jsonrpc.JSONRPCError); ok {
@@ -843,7 +843,7 @@ func processMcpMessage(ctx context.Context, body []byte, s *Server, protocolVers
 			span.SetAttributes(attribute.String("error.type", metricErrorType))
 			return "", rpcErr, err
 		}
-		result, err := mcp.ProcessMethod(ctx, protocolVersion, baseMessage.Id, baseMessage.Method, toolset, promptset, s.ResourceMgr, body, header)
+		result, err := mcp.ProcessMethod(ctx, s.enableDraftSpecs, protocolVersion, baseMessage.Id, baseMessage.Method, toolset, promptset, s.ResourceMgr, body, header)
 		if err != nil {
 			span.SetStatus(codes.Error, err.Error())
 			// Set error.type based on JSON-RPC error code

internal/server/mcp/mcp.go

@@ -19,7 +19,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
-	"slices"
 
 	"github.com/googleapis/mcp-toolbox/internal/prompts"
 	"github.com/googleapis/mcp-toolbox/internal/server/mcp/jsonrpc"
@@ -47,10 +46,13 @@ func NotificationHandler(ctx context.Context, body []byte) error {
 
 // ProcessMethod returns a response for the request.
 // This is the Operation phase of the lifecycle for MCP client-server connections.
-func ProcessMethod(ctx context.Context, mcpVersion string, id jsonrpc.RequestId, method string, toolset tools.Toolset, promptset prompts.Promptset, resourceMgr *resources.ResourceManager, body []byte, header http.Header) (any, error) {
+func ProcessMethod(ctx context.Context, enableDraftSpecs bool, mcpVersion string, id jsonrpc.RequestId, method string, toolset tools.Toolset, promptset prompts.Promptset, resourceMgr *resources.ResourceManager, body []byte, header http.Header) (any, error) {
 	switch mcpVersion {
 	case mcputil.VERSION_DRAFT:
-		return vdraft.ProcessMethod(ctx, id, method, toolset, promptset, resourceMgr, body, header)
+		if enableDraftSpecs {
+			return vdraft.ProcessMethod(ctx, id, method, toolset, promptset, resourceMgr, body, header)
+		}
+		return jsonrpc.NewUnsupportedProtocolVersionError(id, mcpVersion)
 	case mcputil.VERSION_20251125:
 		return v20251125.ProcessMethod(ctx, id, method, toolset, promptset, resourceMgr, body, header)
 	case mcputil.VERSION_20250618:
@@ -63,8 +65,3 @@ func ProcessMethod(ctx context.Context, mcpVersion string, id jsonrpc.RequestId,
 		return jsonrpc.NewUnsupportedProtocolVersionError(id, mcpVersion)
 	}
 }
-
-// VerifyProtocolVersion verifies if the version string is valid.
-func VerifyProtocolVersion(version string) bool {
-	return slices.Contains(mcputil.SUPPORTED_PROTOCOL_VERSIONS, version)
-}

internal/server/server.go

@@ -61,6 +61,7 @@ type Server struct {
 	sseManager          *sseManager
 	ResourceMgr         *resources.ResourceManager
 	mcpPrmFile          string
+	enableDraftSpecs    bool
 }
 
 func InitializeConfigs(ctx context.Context, cfg ServerConfig) (
@@ -403,6 +404,11 @@ func NewServer(ctx context.Context, cfg ServerConfig) (*Server, error) {
 		ResourceMgr:         resourceManager,
 		toolboxUrl:          cfg.ToolboxUrl,
 		mcpPrmFile:          cfg.McpPrmFile,
+		enableDraftSpecs:    cfg.EnableDraftSpecs,
+	}
+
+	if s.enableDraftSpecs {
+		s.logger.WarnContext(ctx, "Flag --enable-draft-specs is active. Please note that draft specs are subject to breaking changes and will be completely removed (not redirected) once stable MCP specifications are released. Do not use this configuration in production.")
 	}
 
 	// cors