Nexus Exchange MCP Server

An MCP server that exposes the Nexus Exchange API as tools an AI agent (Claude Desktop / Claude Code) can call to read market data and place trades.

It talks to the real, public exchange gateway. Market-data and demo tools work with zero configuration; account and trading tools use HMAC API credentials read from environment variables.

What works today

Most tools now target the direct-indexer /api/v1 surface served at the host root (ENG-4740 — the indexer serves its REST API directly instead of via the gateway REST proxy). The routes that have no /api/v1 equivalent stay on the legacy /api/exchange gateway, which remains live dual-stack (ENG-4751), so nothing breaks. See "Migration to /api/v1" below.

get_deposit_target is wired into the agent flow but returns a clear not_yet_available message rather than faking a result; it lights up when the server-side capability ships.

Migration to /api/v1

Per ENG-4740 the gateway REST proxy is being eliminated: each backend service exposes its own REST API and the indexer serves the exchange surface directly under /api/v1 at the host root. This server calls those routes for the v0.7.1 operations it exposes as tools (see API-surface coverage below).

• Base URL is the host root (https://exchange.nexus.xyz), not the …/api/exchange gateway path. /api/v1/* resolves at the root; the legacy-only routes append /api/exchange. A NEXUS_EXCHANGE_API_URL that still ends in /api/exchange is accepted and normalized.
• HMAC signs the full path the server verifies — e.g. /api/v1/orders for v1 routes, the bare route (/orders) for legacy ones.
• cancel_order requires market_id when cancelling a single order (the v1 route marks it required); market_id is optional with cancel_all to scope a mass-cancel to one market.
• Stay on the legacy gateway (no /api/v1 route): list_market_specs, get_market_risk_params, get_order (v1 mounts only PATCH + DELETE on /orders/{id}), get_withdrawals, list_deposits, get_funding_payments, get_adl_history, get_market_adl_events, deposit_collateral, submit_deposit, claim_faucet, adjust_isolated_margin, the agent / api-key / admin-tier tools, get_ws_token*, get_health, get_readiness, get_service_status, and the demo/* reads.

API-surface coverage

The tool surface covers 53 of the 62 distinct operations in Exchange API spec v0.7.1 (92 spec operations counting the /api/v1 aliases of the legacy routes; each aliased pair is one tool).

The pin advanced from v0.6.2 to v0.7.1 as a pin-only bump (ENG-6038); no new tools were added, so the v0.7.1 additions are not yet exposed — tracked in ENG-6136:

• Account cancel-on-disconnect — GET / PUT /account/cancel-on-disconnect.
• /api/v1/bridge Phase A — bridge assets, deposit addresses, and deposit tracking (five operations).
• TrailingLimit order type — a new place-order request variant (a schema addition on the already-mapped order endpoint, so it changes no route count).

Of the remaining gap, the WebSocket upgrade endpoints GET /ws and GET /stream are unmapped by design: a request/response MCP tool cannot hold a streaming socket open, so the server instead mints the auth token (get_ws_token / get_ws_token_legacy) the caller uses to connect to them directly. Separately, v0.7.1 drops the standalone /health and /ready liveness routes (only /status remains), so get_health / get_readiness now call routes the pinned spec no longer documents — reconciliation is folded into ENG-6136.

Authorization tiers

• Public — no credentials.
• HMAC (key + direct gateway) — account reads, trading, agent/funding actions. Uses NEXUS_EXCHANGE_API_KEY / NEXUS_EXCHANGE_API_SECRET. See the "Authentication" note below about the public proxy.
• Caller signature — login (EIP-191) and register_agent (EIP-712) carry a wallet signature the caller produces externally; this server never holds a wallet key and cannot sign for you.
• Session token — the *_api_key tools authenticate with a Bearer session token from login, set as NEXUS_EXCHANGE_SESSION_TOKEN.
• Admin (opt-in) — list_tiers / set_tier / delete_tier use the operator admin secret and mutate other accounts' fee tiers. They are not registered unless NEXUS_EXCHANGE_ENABLE_ADMIN_TOOLS=1 is set (and NEXUS_EXCHANGE_ADMIN_SECRET provided). Never enable these on an untrusted agent surface.

Destructive tools (revoke_agent, delete_api_key, delete_tier, and cancel_order's mass-cancel) require an explicit confirm: true / cancel_all: true flag so a stray call can't do damage by accident.

Quick start

npm install
npm run build
npm start          # runs the stdio MCP server

npm start waits on stdio for an MCP client; it is meant to be launched by Claude rather than run by hand. To verify it works end-to-end against the live API without a client, use the smoke check:

npm run smoke      # lists tools, calls list_markets against production

Expected output ends with list_markets OK -> N markets.

Environment variables

Copy .env.example and set as needed. Only trading/account tools need credentials — never commit real secrets.

API version

Currently targets Exchange API spec v0.7.1.

The pinned version lives in .api-version; the spec itself is published by nexus-xyz/nexus-exchange-api. This repo does not vendor a copy — the drift CI job fetches the pinned release to check for drift, and the scheduled api-version-sync workflow opens a PR when a newer spec releases. The line above is bot-managed; everything around it is human-owned.

Every upstream request also sends this pin as an X-Nexus-Api-Version: <tag> header (e.g. X-Nexus-Api-Version: v0.7.1), alongside a normalized User-Agent: nexus-exchange-mcp/<version>, so the exchange edge can attribute and segment usage by client and by the contract version this server targets. The header value is the server's own compiled-against tag — it is baked in at build time (a test keeps it equal to .api-version), so it is never taken from caller input.

Authentication

Signed requests use the same canonical HMAC-SHA256 scheme the indexer verifies (backend/services/indexer/src/auth.rs):

<timestamp>\n<METHOD>\n<path>\n<query>\n<sha256hex(body)>

signed with the hex-decoded secret and sent as x-signature alongside x-api-key and x-timestamp.

For /api/v1 routes the signed path includes the prefix (e.g. /api/v1/orders); for legacy gateway routes it is the bare path (e.g. /orders). The client signs whatever path it sends, which is exactly what the indexer verifies over.

Important: the public production host still fronts authenticated requests with a proxy that signs with the site's own frontend key, so per-caller HMAC headers are not honored there — authenticated tools resolve to the site account, not yours. To trade as a specific account, point NEXUS_EXCHANGE_API_URL at a direct indexer gateway that verifies client HMAC (for example a local http://localhost:9090 from the exchange docker-compose). Until then, use the public get_demo_* tools to demo the account flow with no secrets.

Claude Desktop config

Add this to your Claude Desktop config (~/Library/Application Support/Claude/claude_desktop_config.json on macOS), adjusting the absolute path to this package's dist/index.js:

{
  "mcpServers": {
    "nexus-exchange": {
      "command": "node",
      "args": ["/ABSOLUTE/PATH/TO/nexus-exchange-mcp/dist/index.js"],
      "env": {
        "NEXUS_EXCHANGE_API_URL": "https://exchange.nexus.xyz"
      }
    }
  }
}

To enable trading, add NEXUS_EXCHANGE_API_KEY / NEXUS_EXCHANGE_API_SECRET to the env block and set NEXUS_EXCHANGE_API_URL to a direct gateway.

Demo script

1. Add the config above, restart Claude Desktop, and confirm nexus-exchange appears in the tools list.
2. Ask: "Show me the BTC market on Nexus" — Claude calls list_markets / get_ticker and reports the live BTC-USDX-PERP price.
3. Ask: "What's in the demo account and its open positions?" — Claude calls get_demo_account and get_demo_positions against the live exchange.

Hosted HTTP server (remote MCP)

The stdio server above runs locally and holds your API key on your machine. The hosted Streamable HTTP server is the remote front door: it lets a trader add Nexus as a remote MCP server without running any key-holding software locally.

npm run build
npm run start:http   # listens on :8080, MCP endpoint at /mcp, probe at /healthz

Behind a TLS-terminating ingress this is the public endpoint https://mcp.exchange.nexus.xyz/mcp. A client adds it with:

claude mcp add --transport http nexus https://mcp.exchange.nexus.xyz/mcp

It exposes the same tool surface as the stdio server — both transports register the identical ToolDef[] from src/tools/ via createServerForClient in src/server.ts, so the tools never drift. The transport is the SDK's StreamableHTTPServerTransport in stateful mode (one MCP session per mcp-session-id), which also serves the SSE fallback stream for server→client messages. Hosted traffic keeps the same nexus-exchange-mcp/<version> User-Agent as the stdio CLI but appends a (http) comment (nexus-exchange-mcp/<version> (http)) so usage attributes to the hosted MCP in the dashboard while still segmenting under one product and version.

Authentication (MVP — no OAuth yet)

OAuth 2.1 is out of scope for this MVP (tracked under the hardening work, ENG-3598, and scoped-key minting, ENG-3486). Until that lands, the hosted server takes the caller's existing Exchange HMAC credential as request headers, captured once at session initialize and reused for the session:

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X-Nexus-Api-Key:    <hmac key id>
X-Nexus-Api-Secret: <hmac secret, hex>

These are deliberately not named x-api-key / x-signature (the upstream gateway's own headers) to avoid confusion. With no credential headers a session still serves public market-data tools and falls back to any server-env credentials. Open question for review: header passthrough is the simplest defensible MVP, but the long-term answer is OAuth-minted scoped (trade-not-withdraw) keys so the caller never hands us a raw secret — see ENG-3598 / ENG-3486.

Development

npm run format     # prettier --write
npm run lint       # eslint
npm run typecheck  # tsc --noEmit
npm test           # unit tests (HMAC scheme, arg mapping, schemas)
npm run test:coverage # unit tests + coverage (text/lcov/json-summary); CI emits the %
npm run smoke      # live end-to-end check against the gateway

License

Dual-licensed under MIT or Apache-2.0, at your option — same as the other Nexus Exchange SDKs.