Sequential Thinking MCP Server

Implements a structured thinking tool that allows LLM clients to decompose complex problems into sequential reasoning steps with explicit branching, revision, and hypothesis tracking. The server exposes a single MCP tool that clients invoke to create hierarchical thought structures where each step can spawn multiple branches representing alternative reasoning paths, enabling non-linear exploration of solution spaces while maintaining full audit trails of the reasoning process.

Implements the MCP tool capability primitive by registering a structured tool schema that defines the reasoning interface (step creation, branching, revision operations) and handling tool invocation requests from MCP clients via JSON-RPC protocol. The server uses TypeScript SDK abstractions to define tool parameters (problem statement, step content, branch metadata) with JSON schema validation, then routes incoming tool calls to internal reasoning handlers that construct and return thought tree structures.

Manages an in-memory hierarchical data structure representing reasoning steps as nodes with parent-child relationships, supporting operations like step creation, branching (creating sibling alternatives), revision (updating step content), and hypothesis labeling. The server maintains tree state during a session, allowing clients to reference previous steps by ID when creating new branches, and provides mechanisms to traverse the tree structure to retrieve reasoning history and branch relationships.

Tracks modifications to reasoning steps and maintains metadata about hypothesis alternatives, allowing clients to record when a step is revised, why it was changed, and which hypotheses were explored or abandoned. The server stores revision history and hypothesis labels alongside step content, enabling clients to query the reasoning trajectory and understand decision points where the LLM chose one path over alternatives.

Implements the MCP server lifecycle including initialization, client connection handling, and graceful shutdown, using the TypeScript SDK's server abstractions. The server registers itself with the MCP protocol, advertises its capabilities (tools, resources, prompts) to connecting clients, and maintains session state for each connected client. Handles transport-level concerns like JSON-RPC message routing and error propagation through the MCP protocol layer.

Serializes hierarchical thought trees and reasoning metadata into JSON structures that MCP clients can consume, parse, and integrate into their own reasoning workflows. The server formats tool responses as structured JSON containing step IDs, branch relationships, content, and metadata, enabling clients to reconstruct the reasoning tree, visualize it, or feed it back into subsequent reasoning iterations. Supports round-trip serialization where clients can submit previous reasoning context to continue or refine reasoning.

Serves as an official reference implementation for MCP server developers, demonstrating TypeScript SDK usage patterns, proper tool registration, error handling, and protocol compliance. The codebase is intentionally simplified and well-documented to serve as a learning resource for developers building their own MCP servers, rather than a feature-complete production system. Includes examples of how to structure tool handlers, manage server state, and respond to client requests according to MCP specifications.