A Model Context Protocol server that exposes the three.ws Pay-As-You-Learn tutor ledger over stdio. Read a tutoring session's itemized tab — one line item per answered question, with per-item cost and a running total — and close the session to seal an attested invoice.

The tutor bills per answered question; this server's tools are free. Viewing the running tab and closing the session never charge the learner — a learner must never pay to see what they owe or to end the session. Sessions are addressed by an opaque sessionId, so no API key and no signer are required — point THREE_WS_BASE at a deployment and go.

Install

npm install @three-ws/tutor-mcp

Or run with npx (no install):

npx @three-ws/tutor-mcp

Quick start

Claude Code, one line:

claude mcp add tutor -- npx -y @three-ws/tutor-mcp

Claude Desktop / Cursor (claude_desktop_config.json or mcp.json):

{
	"mcpServers": {
		"tutor": {
			"command": "npx",
			"args": ["-y", "@three-ws/tutor-mcp"]
		}
	}
}

Inspect the surface with the MCP Inspector:

npx -y @modelcontextprotocol/inspector npx @three-ws/tutor-mcp

Tools

| Tool | Type | What it does | | --------------- | ----- | ---------------------------------------------------------------------------------------------------------------------------- | | load_session | read | Read a session's itemized running tab by sessionId — line items (question, level, tokens, cost), status, and running total. | | close_session | write | Finalize a session and return its attested invoice — seals the ledger with a SHA-256 attestation and locks further billing. |

Both tools are free and move no funds: the per-question answers are the paid action (handled elsewhere). load_session reads live data — the tab grows as questions are billed, so it is not idempotent. close_session mutates state (open → closed) but is itself idempotent: re-closing returns the same itemized total.

Input parameters

load_session — sessionId (required, ≤100 chars).

close_session — sessionId (required, ≤100 chars).

Example

// load_session
> { "sessionId": "learn-abc123" }
{
  "ok": true,
  "sessionId": "learn-abc123",
  "status": "open",
  "createdAt": "2026-06-24T03:40:00.000Z",
  "questionCount": 2,
  "lineItems": [
    { "n": 1, "question": "What is a Solana PDA?", "level": "intro", "outputTokens": 180, "costAtomics": 10000, "costUsd": "0.010000", "at": "2026-06-24T03:41:00.000Z" },
    { "n": 2, "question": "How do CPIs work?", "level": "intro", "outputTokens": 220, "costAtomics": 10000, "costUsd": "0.010000", "at": "2026-06-24T03:42:00.000Z" }
  ],
  "totalAtomics": 20000,
  "totalUsd": "0.020000"
}

// close_session
> { "sessionId": "learn-abc123" }
{
  "ok": true,
  "sessionId": "learn-abc123",
  "createdAt": "2026-06-24T03:40:00.000Z",
  "closedAt": "2026-06-24T03:45:00.000Z",
  "questionCount": 2,
  "lineItems": [ /* same itemized line items */ ],
  "totalAtomics": 20000,
  "totalUsd": "0.020000",
  "attestation": "sha256:…"
}

A sessionId with no stored history returns an empty open session (questionCount: 0) rather than an error — an honest "nothing billed yet", not a failure.

Requirements

• Node.js >= 20.
• Network access to https://three.ws (or your own THREE_WS_BASE).

Environment variables

| Variable | Required | Default | | --------------------- | -------- | ------------------ | | THREE_WS_BASE | no | https://three.ws | | THREE_WS_TIMEOUT_MS | no | 20000 |

Links

• Homepage: https://three.ws
• Changelog: https://three.ws/changelog
• Issues: https://github.com/nirholas/three.ws/issues
• License: Apache-2.0 — see LICENSE