MCP Server

The Stablecoin Harness MCP server lets an LLM agent drive a merchant account end-to-end. It talks to the same HTTP API the dashboard uses, with the same auth surface (email-OTP → SIWE → JWT). Any MCP-compatible client (Claude Code, Claude Desktop, Cursor, your own agent) can connect over stdio and run merchant operations on your behalf.

Why MCP

One-time human step. The merchant authenticates once with email + OTP through the agent; after that the agent operates without re-entering OTP for the lifetime of each credential.
Local-first. The server runs on your machine over stdio. Credentials are stored encrypted at rest and never relayed through StablecoinX infrastructure.
Same surface as the dashboard. Anything a merchant can do in the dashboard, the MCP can do — there is no separate API.

Install

npx @stablecoinx/mcp setup

Source: github.com/e2xlabs/stablecoinx-mcp · npm: @stablecoinx/mcp.

Configuration

With npx @stablecoinx/mcp setup there is nothing to configure — the API endpoint, login chain, and a freshly generated state passphrase are registered for you.

For a manual install, the only input is the state passphrase:

Env var	Required	Purpose
`SCX_STATE_PASSPHRASE`	yes (manual)	Derives the aes-256-gcm key for the encrypted local state file. `setup` generates one for you; set it yourself when installing manually, and reuse the same value across runs to keep the state.
`SCX_STATE_DIR`	no	Override the default state-dir location.

There is no API key, endpoint, or other connection setting to configure — the API key is issued during onboarding and stored encrypted locally; everything else is baked into the package.

Credential model

Credential	How obtained	Lifetime
JWT	email-OTP → SIWE → `POST /v1/auth/verify`	24 h, then re-OTP
*API key `sk_`**	`api_key_create` during onboarding	until revoked
Session key	`session_key_create` (local EOA added to the smart account)	configurable (default 30 days)

After 24 h the JWT expires and dashboard-style tools return RE_AUTH_REQUIRED — the agent prompts for OTP again. The API key and session key survive; only the JWT refreshes. Removing a session key (removeSessionKey on the smart account) requires an admin re-OTP — that’s the panic button.

Tools

Tools are flat, named by resource. The current set:

Group	Tools
Auth	`auth_send_otp`, `auth_verify_otp`, `auth_status`, `auth_logout`
API keys	`api_key_create`, `api_keys_list`, `api_keys_revoke`
Session keys	`session_key_create`
Merchant	`merchant_get`, `merchant_update`
Sessions	`sessions_create_dashboard`, `sessions_get`, `sessions_list`
Paymaster	`paymaster_clients_list/create/update/revoke`, `paymaster_allowlist_list/add/remove`, `paymaster_usage_get`
Webhooks	`webhooks_create`, `webhooks_list`, `webhooks_delete`, `webhooks_deliveries`, `webhooks_rotate_secret`

On-chain treasury operations (yield deposits, Ethena cooldown, etc.) are a planned later phase and are not in the current tool set.

Privacy posture

The server runs on your machine; tool calls don’t round-trip through a third party.
Credentials live in an aes-256-gcm-encrypted state file unlocked by SCX_STATE_PASSPHRASE.
The MCP is a first-class client of the same auth surface as the browser — there is no separate agent audience or scope on the API side. Constraining the agent is a client-side concern (per-tool confirmation prompts).

MCP API reference — per-tool inputs and outputs.
For agents → llms.txt — how to consume these docs as an LLM.