MCP Specification Gap Analysis

Raku MCP SDK vs MCP Specification 2025-11-25

This document compares the current implementation of the Raku MCP SDK against the MCP Specification 2025-11-25 and identifies missing features.

Summary

Table of Contents

• Detailed Analysis

  • Base Protocol

  • Transports

  • Server Features

  • Client Features

  • Utilities

  • Authorization (2025-03-26+)

  • New Features in 2025-11-25

  • Comparison with Python SDK

• Priority Recommendations

  • High Priority (Core Functionality)

  • Medium Priority (Enhanced Functionality)

  • Lower Priority (Advanced Features)

• Protocol Version

• Test Coverage Gaps

• Conclusion

Detailed Analysis

Base Protocol

✅ Implemented

• JSON-RPC 2.0 message format (MCP::JSONRPC)

• Request/Response/Notification handling

• ID generation

• Error codes (ParseError, InvalidRequest, MethodNotFound, InvalidParams, InternalError)

Notes

• Lifecycle: Initialize/initialized handshake with version negotiation (server falls back to latest supported version if client's isn't recognized)

• JSON-RPC batching: Not supported (removed from spec in 2025-06-18)

Transports

✅ Stdio Transport (MCP::Transport::Stdio)

• Complete implementation

• Proper newline-delimited JSON messages

✅ Streamable HTTP Transport (MCP::Transport::StreamableHTTP)

• Full server-side implementation (POST/GET/DELETE)

• Full client-side implementation

• Session management (MCP-Session-Id header)

• Last-Event-ID replay for SSE resumption

• CORS handling via allowed-origins

• Protocol version validation (MCP-Protocol-Version header)

• Proper error responses per spec (400, 403, 404, 405, 406, 415)

✅ Legacy SSE Transport (MCP::Transport::SSE)

• Server-side: GET /sse for SSE stream, POST /message for client messages

• Client-side: connects to SSE endpoint, receives POST URL via endpoint event

• Origin validation

• Single-client model (one SSE connection at a time)

Server Features

✅ Tools (MCP::Server::Tool)

• Tool registration with name, description, schema

• Tool calling with arguments

• Builder pattern API

• Tool annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint)

• outputSchema for structured tool outputs (2025-06-18)

• Tool name validation (SEP-986: ^[a-zA-Z0-9_-]{1,64}$)

• tools/list pagination support

✅ Resources (MCP::Server::Resource)

• Resource registration with URI, name, description, mimeType

• Resource reading

• Resource templates (URI templates with placeholders)

• Resource subscriptions (resources/subscribe, resources/unsubscribe)

• notifications/resources/list_changed and notifications/resources/updated

• resources/list pagination support

• Resource annotations (audience, priority)

✅ Prompts (MCP::Server::Prompt)

• Prompt registration with arguments

• Prompt retrieval with argument substitution

• prompts/list pagination support

• notifications/prompts/list_changed

Client Features

✅ Sampling (MCP::Client sampling-handler) - Implemented

• sampling/createMessage handling with full parameter support

• Tool definitions in sampling requests (SEP-1577)

• toolChoice parameter support

• includeContext parameter with capability validation

• stopReason in responses

• Tool validation in sampling messages

• Server-side create-message() convenience method with tools/toolChoice/includeContext

✅ Roots - Implemented

• Root type with uri and optional name

• Client-side:

  • roots configuration option

  • Handles roots/list requests from server

  • set-roots() method sends notifications/roots/list_changed

  • Advertises roots capability (with listChanged)

• Server-side:

  • list-roots() method to request roots from client

✅ Elicitation (2025-06-18 feature)

• ElicitationCapability with form/url mode support

• ElicitationAction enum (accept/decline/cancel)

• ElicitationResponse type with content

• Server-side:

  • elicit(message, schema) for form mode requests

  • elicit-url(message, url, elicitation-id) for URL mode

  • notify-elicitation-complete(elicitation-id) for completion

• Client-side:

  • elicitation-handler callback for handling requests

  • Capability negotiation with form/url modes

  • URLElicitationRequired error code (-32042)

Utilities

✅ Progress Tracking - Implemented

• progress() method on Server with automatic _meta.progressToken extraction

• proto dispatch-request sets $*MCP-PROGRESS-TOKEN dynamic variable for all handlers

• Explicit token parameter overrides implicit _meta token

• No notification emitted when no token is available

• Client progress() Supply emits typed Progress objects from notifications/progress

• Types defined (Progress)

✅ Logging - Implemented

• log() method on Server with level filtering

• LogLevel enum, LogEntry type, parse-log-level, log-level-at-or-above helpers

• logging/setLevel request handler on Server stores and applies log level

• Log notifications below configured level are suppressed

• Client set-log-level() method sends logging/setLevel request

✅ Cancellation - Implemented

• Server tracks in-flight requests and handles notifications/cancelled

• Client sends cancellation notification on timeout

• Both sides have cancel-request method for explicit cancellation

• is-cancelled method for handlers to check cancellation status

✅ Ping

• Server responds to ping requests

• Client has ping() helper

✅ Completion (autocomplete)

• completion/complete request handling

• Server: add-prompt-completer(), add-resource-completer() for registering completers

• Client: complete-prompt(), complete-resource() convenience methods

• CompletionResult type with values, total, hasMore

• Auto-truncation to 100 values per spec

• completions capability advertised when completers registered

Authorization (2025-03-26+)

✅ Implemented

OAuth 2.1 authorization framework:

• ✅ OAuth 2.1 with PKCE (S256)

• ✅ Token refresh

• ✅ Resource indicators (RFC 8707)

• ✅ Authorization server metadata discovery (RFC 8414 + OIDC fallback)

• ✅ Protected resource metadata (RFC 9728)

• ✅ Server-side token validation with WWW-Authenticate headers

• ✅ Client-side automatic token management and 401 retry

• ✅ Dynamic client registration (RFC 7591)

New Features in 2025-11-25

✅ Tasks (Experimental)

Long-running operation support:

• Task creation with task hint in tools/call

• Task states: working, input_required, completed, failed, cancelled

• tasks/get for status polling

• tasks/cancel for cancellation

• tasks/result for blocking result retrieval

• tasks/list for listing all tasks

• notifications/tasks/status on state changes

• Tool-level execution.taskSupport via builder

✅ Extensions Framework

• Extension capability negotiation via experimental hash

• Extension settings and versioning

• Namespaced extension methods and notification dispatch

• Server: register-extension(), unregister-extension()

• Client: register-extension(), server-extensions(), supports-extension()

✅ Authorization Extensions

• ✅ SEP-1046: OAuth client credentials (M2M) — OAuthM2MClient with client_credentials grant

• ✅ SEP-990: Enterprise IdP policy controls — OAuthEnterpriseClient with token exchange (RFC 8693) and JWT bearer grant (RFC 7523)

✅ URL Mode Elicitation (SEP-1036)

• elicit-url() method for URL mode requests

• notify-elicitation-complete() for completion notifications

• URLElicitationRequired error code (-32042)

✅ Sampling with Tools (SEP-1577)

• Tool definitions in sampling requests

• Server-side agentic loops

Comparison with Python SDK

The official Python SDK implements:

Remaining Work

All priority items from the original roadmap have been completed, including expanded test coverage for progress tracking, error edge cases, and concurrent operations.

Protocol Version

Current implementation targets: 2025-11-25 ✅

All key features for 2025-11-25 compliance are implemented.

Test Coverage Gaps

Current tests cover:

• ✅ Types serialization (01-types)

• ✅ JSON-RPC encoding/decoding (02-jsonrpc)

• ✅ Builder patterns (03-builders)

• ✅ Transport interface (04-transport)

• ✅ Server dispatch and lifecycle (05-server)

• ✅ Client initialization (06-client)

• ✅ Top-level MCP exports (07-mcp)

• ✅ Sampling validation (08-sampling)

• ✅ HTTP transport (09-http-transport)

• ✅ OAuth 2.1 types, PKCE, server/client handlers (10-oauth)

• ✅ Tasks framework (11-tasks)

• ✅ Extensions framework (12-extensions)

• ✅ Resource templates (13-resource-templates)

• ✅ SSE transport (14-sse-transport)

Areas with limited test coverage:

• Progress tracking (server notifications, client Supply)

• Error edge cases (malformed messages, transport failures)

• Concurrent operations (parallel requests, race conditions)

Conclusion

The Raku MCP SDK provides comprehensive MCP specification 2025-11-25 coverage. All transport types (Stdio, Streamable HTTP, Legacy SSE), all server features (Tools, Resources, Prompts), all client features (Sampling, Roots, Elicitation, Completion), and full OAuth 2.1 authorization are implemented. No significant gaps remain.