@three-ws/agentcore-payments-mcp

MCP server for three.ws Agent Payment Sessions — govern agent x402 spending without exposing private keys.

Concept

The agent does not hold a wallet. It proposes spend. Governance enforces policy.

A Payment Session is a budget envelope you fund once from your three.ws credits. You hand an agent the session bearer token; the agent calls paid x402 endpoints through this server. The platform's wallet signs every transaction. The session's allowlist, per-transaction ceiling, and total budget are enforced atomically on the server — the agent can never overspend.

Quick start

# Configure
export THREE_WS_SESSION="<the value of your __Host-sid cookie>"
export PAYMENT_SESSION_TOKEN="pss_<session-id>_<random>"

# Run
npx @three-ws/agentcore-payments-mcp

MCP client config (~/.cursor/mcp.json, Claude Desktop, etc.):

{
  "mcpServers": {
    "three-ws-payments": {
      "command": "npx",
      "args": ["-y", "@three-ws/agentcore-payments-mcp"],
      "env": {
        "THREE_WS_SESSION": "<the value of your __Host-sid cookie>",
        "PAYMENT_SESSION_TOKEN": "pss_..."
      }
    }
  }
}

Environment variables

Tools

create_payment_session

Create a new session funded from your credits.

{
  "budget_usd": 10.00,
  "label": "Research agent — June sprint",
  "expiry_seconds": 86400,
  "max_per_tx_usd": 0.50,
  "allowed_hosts": ["api.example.com", "data.provider.io"],
  "network": "solana"
}

Returns { session, token }. The token is shown once — store it immediately.

pay_with_session

Pay an x402 endpoint using a session token. The platform wallet signs; your session's policy is enforced.

{
  "url": "https://api.example.com/data",
  "method": "GET",
  "session_token": "pss_...",
  "idempotency_key": "run-42-fetch-data"
}

Returns { ok, paid, result, payment, session } with the tx hash, explorer link, and updated budget.

If session_token is omitted, the PAYMENT_SESSION_TOKEN env var is used.

check_payment_session

Inspect a session's budget, status, and recent payments.

{ "session_id": "...", "include_executions": true }

list_payment_sessions

List all sessions for the authenticated user, with aggregate stats.

{ "status": "active", "limit": 20 }

cancel_payment_session

Cancel a session and refund the un-spent budget to your credits.

{ "session_id": "..." }

Network support

Integrating with @three-ws/x402-mcp

The existing pay_and_call tool in @three-ws/x402-mcp now accepts session_token directly:

{
  "url": "https://api.example.com/endpoint",
  "session_token": "pss_...",
  "confirm": true
}

This routes the payment through /api/pay/execute instead of signing locally — the session's governance policy applies.

Examples

Runnable, no-payment examples live in examples/:

node examples/list-tools.mjs       # every tool with its schema and safety annotations
node examples/plan-a-session.mjs   # read live x402 prices, print the policy to authorize

Neither one holds a wallet, reads a credential, or calls pay_with_session, so nothing is signed and nothing is spent. plan-a-session.mjs is the habit worth copying: read what an endpoint actually charges before you decide what budget to authorize. See examples/README.md.

Session lifecycle

create (budget debited from credits)
  └─ active → pay_with_session calls spend against budget
       ├─ exhausted (budget fully consumed)
       ├─ expired (TTL elapsed — cron refunds remaining budget)
       └─ cancelled (manual — remaining budget refunded immediately)

Programmatic use

The package entry point exports TOOLS (every tool definition: name, title, description, inputSchema, annotations, handler) and buildServer(), which returns a fully-registered McpServer with no transport attached. Importing is side-effect free and needs no credential, so you can mount these tools inside a host of your own or inspect the surface offline; a credential is only required when a handler actually runs.

// run with: THREE_WS_SESSION=<your __Host-sid value> node this-file.mjs
import { TOOLS, buildServer } from '@three-ws/agentcore-payments-mcp';

for (const tool of TOOLS) {
	const kind = tool.annotations.readOnlyHint ? 'read ' : 'write';
	console.log(`${kind} ${tool.name}`);
}

// A tool handler is a plain async function against the live API.
const list = TOOLS.find((t) => t.name === 'list_payment_sessions');
console.log(await list.handler({ limit: 3 }));

// Or hand the whole registered server to your own MCP transport.
buildServer();

Security properties

• No key exposure: the session token is a time-bounded, HMAC-signed grant. Compromising it lets an attacker spend up to the remaining budget at allowed hosts — nothing more.
• Atomic budget enforcement: concurrent payments use a SQL UPDATE … WHERE remaining >= amount RETURNING — two simultaneous requests can never collectively overspend.
• Allowlist: if allowed_hosts is set, the governor rejects any request to a host not on the list before signing.
• Per-transaction cap: max_per_tx_usd prevents a single large payment draining the entire budget.
• SSRF protection: all x402 target URLs are validated against a public-IP allowlist and DNS-resolved server-side before any payment is signed.