Sequential Thinking MCP Server
github.com/modelcontextprotocol/servers-sequentialthinking- Category
- Developer Tools
- Rank
- No. 673Tools index
- Pricing
- Free
- Type
- TOOL
- Use case
- Agent Building
- Interfaces
- MCP
- Builder
- modelcontextprotocol
- GitHub
- 90.6k stars
- Latest release
- 2026.8.31
- Date
About
The reference MCP server for structured step-by-step reasoning: lets an agent break a problem into revisable thought steps and branch alternatives before answering.
What it does
This MCP service records numbered reasoning entries during an agent session. Each entry can revise an earlier idea, start a named branch, or extend the estimated length. The service keeps session history in memory, optionally prints formatted thoughts to standard error, and returns progress metadata rather than a final solution itself.
Why it's ranked here
Its compact implementation makes the protocol mechanics easy to understand, and its flexible numbering, revision, and branching fields support changing plans. The repository explicitly presents it as an educational reference, not a production-ready service. That framing matters because state is temporary and the exposed capability depends heavily on the calling agent using the fields correctly.
What's good
Input validation accepts numeric strings, handles textual booleans safely, and rejects invalid thought numbers. The service automatically expands the estimated total when a sequence runs long. It tracks named branches and returns both text and structured progress data. Thought logging can be disabled through an environment setting, which helps operators avoid printing reasoning content.
Tradeoffs
History and branches live only in process memory, with no persistence or retrieval interface. The server exposes only standard input and output transport. It records revisions and branches but does not verify that referenced thoughts exist. Its read-only and idempotent annotations are questionable because every accepted entry mutates session history and repeated submissions increase its length.
How to use it well
Use it as a small teaching example or as temporary reasoning scaffolding for an MCP client handling complex planning and course corrections. It suits sessions where the agent can consistently number entries and stop deliberately. It does not provide durable memory, external facts, file access, execution, or independent validation of the resulting answer.
Technical notes+
src/sequentialthinking/index.ts creates an McpServer, registers the sequentialthinking tool with Zod schemas, returns structuredContent, and connects through StdioServerTransport. Its coercedBoolean preprocessor recognizes boolean values plus the strings true and false; numeric fields use integer coercion with a minimum of one. src/sequentialthinking/lib.ts stores thoughtHistory and branches in memory, raises totalThoughts when needed, formats Chalk output to stderr, and honors DISABLE_THOUGHT_LOGGING. src/sequentialthinking/vitest.config.ts targets Node and looks for Vitest cases under **/__tests__/**/*.test.ts. The root package.json defines npm workspaces under src/* and depends on @modelcontextprotocol/server-sequential-thinking.
Observed
- License
- Apache License 2.0 for new contributions, with existing code under MIT.
- Primary language
- TypeScript.
- Packaging
- npm workspace package exposed as @modelcontextprotocol/server-sequential-thinking and usable through npx.
- Interface
- MCP tool server using standard input and output transport.
- Runtime state
- Thought history and branch records are stored in process memory.
- Validation
- Zod validates and coerces the tool input, including integers and boolean strings.
Read from README.md, package.json, src/memory/index.ts, src/filesystem/lib.ts, src/everything/index.ts, src/filesystem/index.ts, src/memory/vitest.config.ts, src/filesystem/path-utils.ts, src/sequentialthinking/lib.ts, src/filesystem/roots-utils.ts, src/sequentialthinking/index.ts, src/everything/vitest.config.ts, src/filesystem/vitest.config.ts, src/filesystem/path-validation.ts, src/sequentialthinking/vitest.config.ts.
Tech Stack
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