Thoughtbox

A reasoning ledger for AI agents. Thoughtbox is an MCP server that provides structured reasoning tools, enabling agents to think step-by-step, branch into alternative explorations, revise earlier conclusions, and maintain a persistent record of their cognitive process.

Unlike ephemeral chain-of-thought prompting, Thoughtbox creates a durable reasoning chain — a ledger of thoughts that can be visualized, exported, and analyzed. Each thought is a node in a graph structure supporting forward thinking, backward planning, branching explorations, and mid-course revisions.

Observatory UI showing a reasoning session with 14 thoughts and a branch exploration (purple nodes 13-14) forking from thought 5.

Core Concepts

The Reasoning Ledger

Thoughtbox treats reasoning as data, not just process. Every thought is:

• Numbered: Logical position in the reasoning chain (supports non-sequential addition)

• Timestamped: When the thought was recorded

• Linked: Connected to previous thoughts, branch origins, or revised thoughts

• Persistent: Stored in sessions that survive across conversations

• Exportable: Full reasoning chains can be exported as JSON or Markdown

This creates an auditable trail of how conclusions were reached — invaluable for debugging agent behavior, understanding decision-making, and improving reasoning strategies.

Thinking Patterns

Thoughtbox supports multiple reasoning strategies out of the box:

See the Patterns Cookbook for comprehensive examples.

Features

1. Thoughtbox Tool — Structured Reasoning

The core tool for step-by-step thinking with full graph capabilities.

// Simple forward thinking
{ thought: "First, let's identify the problem...", thoughtNumber: 1, totalThoughts: 5, nextThoughtNeeded: true }

// Branching to explore alternatives
{ thought: "Option A: Use PostgreSQL...", thoughtNumber: 3, branchFromThought: 2, branchId: "sql-path", ... }

// Revising an earlier conclusion
{ thought: "Actually, the root cause is...", thoughtNumber: 7, isRevision: true, revisesThought: 3, ... }

Parameters:

• thought (string): The current thinking step

• thoughtNumber (integer): Logical position in the chain

• totalThoughts (integer): Estimated total (adjustable)

• nextThoughtNeeded (boolean): Continue thinking?

• branchFromThought (integer): Fork point for branching

• branchId (string): Branch identifier

• isRevision (boolean): Marks revision of earlier thought

• revisesThought (integer): Which thought is being revised

2. Observatory — Real-Time Visualization

A built-in web UI for watching reasoning unfold in real-time.

Features:

• Live Graph: Watch thoughts appear as they're added

• Snake Layout: Compact left-to-right flow with row wrapping

• Hierarchical Branches: Branches collapse into clickable stub nodes (A, B, C...)

• Navigation: Click stubs to explore branches, back button to return

• Detail Panel: Click any node to view full thought content

• Multi-Session: Switch between active reasoning sessions

Access: The Observatory is available at http://localhost:1729 when the server is running.

3. Mental Models — Reasoning Frameworks

15 structured mental models that provide process scaffolds for different problem types.

Available Models:

• rubber-duck — Explain to clarify thinking

• five-whys — Root cause analysis

• pre-mortem — Anticipate failures

• steelmanning — Strengthen opposing arguments

• fermi-estimation — Order-of-magnitude reasoning

• trade-off-matrix — Multi-criteria decisions

• decomposition — Break down complexity

• inversion — Solve by avoiding failure

• And 7 more...

Operations:

• get_model — Retrieve a specific model's prompt

• list_models — List all models (filter by tag)

• list_tags — Available categories (debugging, planning, decision-making, etc.)

4. Notebook — Literate Programming

Interactive notebooks combining documentation with executable JavaScript/TypeScript.

Features:

• Isolated execution environments per notebook

• Full package.json support with dependency installation

• Sequential Feynman template for deep learning workflows

• Export to .src.md format

Operations: create, add_cell, run_cell, export, list, load, update_cell

Installation

Quick Start

npx -y @kastalien-research/thoughtbox

MCP Client Configuration

Claude Code

Add to your ~/.claude/settings.json or project .claude/settings.json:

{
  "mcpServers": {
    "thoughtbox": {
      "command": "npx",
      "args": ["-y", "@kastalien-research/thoughtbox"]
    }
  }
}

Cline / VS Code

Add to your MCP settings or .vscode/mcp.json:

{
  "servers": {
    "thoughtbox": {
      "command": "npx",
      "args": ["-y", "@kastalien-research/thoughtbox"]
    }
  }
}

Usage Examples

Forward Thinking — Problem Analysis

Thought 1: "Users report slow checkout. Let's analyze..."
Thought 2: "Data shows 45s average, target is 10s..."
Thought 3: "Root causes: 3 API calls, no caching..."
Thought 4: "Options: Redis cache, query optimization, parallel calls..."
Thought 5: "Recommendation: Implement Redis cache for product data"

Backward Thinking — System Design

Thought 8: [GOAL] "System handles 10k req/s with <100ms latency"
Thought 7: "Before that: monitoring and alerting operational"
Thought 6: "Before that: resilience patterns implemented"
Thought 5: "Before that: caching layer with invalidation"
...
Thought 1: [START] "Current state: 1k req/s, 500ms latency"

Branching — Comparing Alternatives

Thought 4: "Need to choose database architecture..."

Branch A (thought 5): branchId="sql-path"
  "PostgreSQL: ACID compliance, mature tooling, relational integrity"

Branch B (thought 5): branchId="nosql-path"
  "MongoDB: Flexible schema, horizontal scaling, document model"

Thought 6: [SYNTHESIS] "Use PostgreSQL for transactions, MongoDB for analytics"

Environment Variables

• DISABLE_THOUGHT_LOGGING=true — Suppress thought logging to stderr

Development

# Install dependencies
npm install

# Build
npm run build

# Development with hot reload
npm run dev

# Run the server
npm start

Architecture

src/
├── index.ts              # MCP server entry point
├── persistence/          # Session and thought storage
│   └── storage.ts        # In-memory storage with linked thought chains
├── observatory/          # Real-time visualization
│   ├── ui/               # Self-contained HTML/CSS/JS
│   ├── ws-server.ts      # WebSocket server for live updates
│   └── emitter.ts        # Event emission for thought changes
├── mental-models/        # 15 reasoning frameworks
├── notebook/             # Literate programming engine
└── resources/            # Documentation and patterns cookbook

License

MIT License — free to use, modify, and distribute.