attribute-based capability declaration with schema auto-generation
Developers declare MCP capabilities (tools, resources, prompts) using PHP attributes (#[McpTool], #[McpResource], #[McpPrompt]) on class methods. The SDK's Discoverer and SchemaGenerator components automatically parse DocBlocks and method signatures using phpdocumentor/reflection-docblock to generate JSON Schema definitions for each capability, eliminating manual schema maintenance. This approach integrates with the Builder pattern to accumulate and register capabilities during server initialization.
Unique: Uses PHP 8.0+ attributes combined with DocBlock reflection to eliminate boilerplate schema definitions, integrating phpdocumentor/reflection-docblock for intelligent parsing of method signatures and documentation. The Builder pattern accumulates these declarations during initialization, creating a single source of truth between code and MCP definitions.
vs alternatives: Eliminates schema duplication compared to Python MCP SDK's manual schema registration, leveraging PHP's native reflection and attributes for tighter code-to-protocol coupling.
builder-pattern server assembly with fluent configuration
The Server\Builder class (src/Server/Builder.php) implements a fluent builder pattern that accumulates MCP server configuration through method chaining. Developers call methods like ->addTool(), ->addResource(), ->addPrompt() to register capabilities, then ->build() constructs the complete Server instance with all dependencies wired. The builder manages capability loaders (ArrayLoader, Discoverer), transport configuration, session stores, and request handlers, providing a single assembly point that enforces initialization order and dependency injection.
Unique: Implements a strict builder pattern that separates configuration accumulation from server instantiation, with explicit transport layer abstraction (StdioTransport, StreamableHttpTransport) and pluggable session stores (PSR-16 compatible). The builder enforces initialization order and provides a single assembly point for all MCP components.
vs alternatives: More flexible than Python SDK's direct Server instantiation because it decouples configuration from construction, enabling runtime transport swapping and easier testing with mock components.
error handling with mcp-compliant error responses
The SDK implements comprehensive error handling that catches exceptions during capability execution and converts them to MCP-compliant error responses with proper error codes and messages. The error handling pipeline includes validation errors (argument schema mismatches), execution errors (capability handler exceptions), and protocol errors (malformed requests). Each error type is mapped to an appropriate MCP error code (e.g., -32600 for invalid request, -32603 for internal error), with detailed error messages for debugging.
Unique: Implements a multi-stage error handling pipeline that catches exceptions at validation, execution, and protocol levels, converting each to MCP-compliant error responses with appropriate error codes. Error messages are structured to provide debugging information while maintaining security.
vs alternatives: More structured than generic exception handling because it explicitly maps error types to MCP error codes, ensuring clients receive properly formatted error responses that comply with the MCP specification.
protocol message routing and json-rpc 2.0 serialization
The Server class implements the core MCP protocol message routing logic, handling JSON-RPC 2.0 serialization and deserialization of all MCP requests and responses. The protocol layer routes incoming requests (tools/call, resources/read, prompts/get, etc.) to appropriate request handlers, manages request/response correlation via JSON-RPC IDs, and handles notifications (one-way messages without response). The transport layer abstracts the underlying communication mechanism (STDIO, HTTP), while the protocol layer remains transport-agnostic.
Unique: Implements JSON-RPC 2.0 protocol routing that maps MCP methods to request handlers, with proper request/response correlation via JSON-RPC IDs and support for notifications. The protocol layer is transport-agnostic, allowing the same routing logic to work with STDIO and HTTP transports.
vs alternatives: More protocol-compliant than ad-hoc message handling because it strictly follows JSON-RPC 2.0 specification, ensuring proper request/response correlation and error handling.
completion provider integration for llm context enhancement
The SDK includes a CompletionProvider capability that allows MCP servers to provide completion suggestions to AI clients, enhancing LLM context with dynamic suggestions based on partial input. Completion providers receive partial text and return a list of completion options with descriptions. This capability is useful for exposing autocomplete functionality, command suggestions, or context-aware recommendations to AI clients. Completion providers are defined similarly to tools and resources, with a handler that generates completions based on input.
Unique: Completion providers are first-class MCP capabilities that allow servers to provide dynamic suggestions to AI clients, enhancing LLM context with autocomplete and recommendation functionality. The execution pipeline validates input and invokes handlers to generate completions.
vs alternatives: More integrated than external autocomplete services because completion providers are built into the MCP protocol, allowing AI clients to discover and use suggestions without additional API calls.
conformance testing and inspector-based validation
The SDK includes built-in testing infrastructure with conformance tests that validate MCP protocol compliance and inspector-based testing that captures and validates server behavior. The Inspector component intercepts all MCP messages (requests, responses, notifications) and records them for analysis. Conformance tests verify that the server correctly implements MCP specification requirements (e.g., proper error codes, valid response formats). This enables developers to validate their MCP servers against the specification without manual testing.
Unique: Provides built-in conformance testing and Inspector-based message capture that enables automated validation of MCP protocol compliance. The Inspector intercepts all messages and the conformance test suite validates against MCP specification requirements, with snapshot-based testing for regression detection.
vs alternatives: More comprehensive than manual testing because it automates protocol compliance validation and captures all messages for analysis, enabling developers to catch specification violations early.
multi-transport protocol abstraction with stdio and http support
The SDK abstracts communication transport through a Transport interface with concrete implementations for STDIO (StdioTransport) and HTTP (StreamableHttpTransport). The Server class routes all MCP protocol messages through the selected transport, handling JSON-RPC 2.0 serialization, message framing, and bidirectional communication. This abstraction allows the same server logic to run in CLI environments (STDIO) or as HTTP endpoints without code changes, with the transport layer managing session lifecycle and connection state.
Unique: Provides a unified Transport interface that abstracts STDIO and HTTP communication, allowing identical server code to run in CLI (Claude Desktop) and HTTP (cloud) contexts. The transport layer manages JSON-RPC 2.0 framing, session lifecycle (via symfony/uid), and bidirectional message routing without exposing protocol details to capability handlers.
vs alternatives: More deployment-flexible than Python SDK's STDIO-first approach, with explicit HTTP support enabling cloud-native MCP server architectures without requiring separate client/server implementations.
capability registry with pluggable loaders and discovery
The Capability\Registry stores all registered tools, resources, and prompts, populated by pluggable loaders (ArrayLoader for manual registration, Discoverer for attribute-based auto-discovery). The registry implements a lookup interface that the Server uses to resolve capability requests by name. Loaders can be chained or composed, allowing hybrid approaches where some capabilities are manually defined and others are auto-discovered from class attributes, with the registry merging results into a unified capability namespace.
Unique: Implements a pluggable loader architecture where ArrayLoader handles manual registration and Discoverer handles attribute-based auto-discovery, with the Registry merging results into a unified namespace. This enables hybrid approaches where capabilities come from multiple sources without code duplication.
vs alternatives: More modular than monolithic registry approaches because loaders are composable and can be extended independently, supporting both declarative (attributes) and imperative (manual) capability registration patterns.
+6 more capabilities