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

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.

API-surface coverage

These tools map to 38 of the 40 operations in the v0.4.0 OpenAPI spec (.api-version). The two intentionally unmapped operations are the WebSocket upgrade endpoints GET /ws and GET /stream — 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.

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

<!-- api-version-sync:start -->

Currently targets Exchange API spec `v0.4.0`.

<!-- api-version-sync:end -->

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.

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.

Important: the default public base URL (/api/exchange) is a proxy that signs with the site's own frontend key, so it does not honor per-caller HMAC headers — authenticated tools through it 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/api/exchange"
      }
    }
  }
}

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.

1. Ask: "Show me the BTC market on Nexus" — Claude calls list_markets /

get_ticker and reports the live BTC-USDX-PERP price.

1. 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 is tagged with a distinct User-Agent (nexus-exchange-mcp-http/...) so usage attributes to "MCP" in the dashboard.

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:

>

``text 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.