Sequential Thinking MCP Server

Instructions

Implementation Reference

• index.ts:91-137 (handler)

  Core execution logic for the sequentialthinking tool: validates and processes thought data, manages history and branches, logs formatted output, returns JSON status.

  public processThought(input: unknown): { content: Array<{ type: string; text: string }>; isError?: boolean } {
    try {
      const validatedInput = this.validateThoughtData(input);
  
      if (validatedInput.thoughtNumber > validatedInput.totalThoughts) {
        validatedInput.totalThoughts = validatedInput.thoughtNumber;
      }
  
      this.thoughtHistory.push(validatedInput);
  
      if (validatedInput.branchFromThought && validatedInput.branchId) {
        if (!this.branches[validatedInput.branchId]) {
          this.branches[validatedInput.branchId] = [];
        }
        this.branches[validatedInput.branchId].push(validatedInput);
      }
  
      if (!this.disableThoughtLogging) {
        const formattedThought = this.formatThought(validatedInput);
        console.error(formattedThought);
      }
  
      return {
        content: [{
          type: "text",
          text: JSON.stringify({
            thoughtNumber: validatedInput.thoughtNumber,
            totalThoughts: validatedInput.totalThoughts,
            nextThoughtNeeded: validatedInput.nextThoughtNeeded,
            branches: Object.keys(this.branches),
            thoughtHistoryLength: this.thoughtHistory.length
          }, null, 2)
        }]
      };
    } catch (error) {
      return {
        content: [{
          type: "text",
          text: JSON.stringify({
            error: error instanceof Error ? error.message : String(error),
            status: 'failed'
          }, null, 2)
        }],
        isError: true
      };
    }
  }

• index.ts:196-241 (schema)

  Input schema defining parameters for the tool call including thought, numbering, branching, and revision flags.

  inputSchema: {
    type: "object",
    properties: {
      thought: {
        type: "string",
        description: "Your current thinking step"
      },
      nextThoughtNeeded: {
        type: "boolean",
        description: "Whether another thought step is needed"
      },
      thoughtNumber: {
        type: "integer",
        description: "Current thought number",
        minimum: 1
      },
      totalThoughts: {
        type: "integer",
        description: "Estimated total thoughts needed",
        minimum: 1
      },
      isRevision: {
        type: "boolean",
        description: "Whether this revises previous thinking"
      },
      revisesThought: {
        type: "integer",
        description: "Which thought is being reconsidered",
        minimum: 1
      },
      branchFromThought: {
        type: "integer",
        description: "Branching point thought number",
        minimum: 1
      },
      branchId: {
        type: "string",
        description: "Branch identifier"
      },
      needsMoreThoughts: {
        type: "boolean",
        description: "If more thoughts are needed"
      }
    },
    required: ["thought", "nextThoughtNeeded", "thoughtNumber", "totalThoughts"]
  }

• index.ts:258-260 (registration)

  Tool registration in the ListToolsRequestHandler, exposing sequentialthinking in the tools list.

  server.setRequestHandler(ListToolsRequestSchema, async () => ({
    tools: [SEQUENTIAL_THINKING_TOOL],
  }));

• index.ts:262-274 (registration)

  CallToolRequestHandler dispatch that routes calls to 'sequentialthinking' to the processThought handler.

  server.setRequestHandler(CallToolRequestSchema, async (request) => {
    if (request.params.name === "sequentialthinking") {
      return thinkingServer.processThought(request.params.arguments);
    }
  
    return {
      content: [{
        type: "text",
        text: `Unknown tool: ${request.params.name}`
      }],
      isError: true
    };
  });

• index.ts:34-61 (helper)

  Helper function to validate and type-check the incoming thought data against ThoughtData interface.

  private validateThoughtData(input: unknown): ThoughtData {
    const data = input as Record<string, unknown>;
  
    if (!data.thought || typeof data.thought !== 'string') {
      throw new Error('Invalid thought: must be a string');
    }
    if (!data.thoughtNumber || typeof data.thoughtNumber !== 'number') {
      throw new Error('Invalid thoughtNumber: must be a number');
    }
    if (!data.totalThoughts || typeof data.totalThoughts !== 'number') {
      throw new Error('Invalid totalThoughts: must be a number');
    }
    if (typeof data.nextThoughtNeeded !== 'boolean') {
      throw new Error('Invalid nextThoughtNeeded: must be a boolean');
    }
  
    return {
      thought: data.thought,
      thoughtNumber: data.thoughtNumber,
      totalThoughts: data.totalThoughts,
      nextThoughtNeeded: data.nextThoughtNeeded,
      isRevision: data.isRevision as boolean | undefined,
      revisesThought: data.revisesThought as number | undefined,
      branchFromThought: data.branchFromThought as number | undefined,
      branchId: data.branchId as string | undefined,
      needsMoreThoughts: data.needsMoreThoughts as boolean | undefined,
    };
  }