@arcnautical/mcp

An MCP server for the ArcNautical API: screen any commercial vessel by IMO number for sanctions, ownership opacity and a vetting grade — from Claude, ChatGPT, Cursor, VS Code, Windsurf or any MCP client.

Two tools need no API key at all. Add it, ask "is IMO 9274446 sanctioned?", get the answer.

Two ways to use it: a remote endpoint at https://mcp.arcnautical.com/mcp (nothing to install — claude.ai, ChatGPT, Claude Code, Cursor) or a local server over stdio with npx -y @arcnautical/mcp (Claude Desktop and every other stdio client).

IMO 9274446 HS STAR: sanctions RED — 4 confirmed matches on vessel identifier.
Ownership opacity MEDIUM. Vetting grade E (unacceptable). Checked 2026-09-12T08:10:40Z.

Remote endpoint (no install)

https://mcp.arcnautical.com/mcp — MCP Streamable HTTP, stateless, JSON responses. No authentication is required for check_vessel and find_port; the keyed tools take your API key as an Authorization: Bearer header on the MCP request (an X-API-Key or arcnautical-api-key header is accepted too, for gateways that name the header themselves — never a query parameter).

claude.ai — Settings → Connectors → Add custom connector → URL https://mcp.arcnautical.com/mcp, no authentication. The two keyless tools are available at once.

ChatGPT — Settings → Connectors → Create (developer mode) → server URL https://mcp.arcnautical.com/mcp, no authentication.

Claude Code

claude mcp add --transport http arcnautical https://mcp.arcnautical.com/mcp
claude mcp add --transport http arcnautical https://mcp.arcnautical.com/mcp --header "Authorization: Bearer arc_live_…"

Cursor — .cursor/mcp.json:

{
  "mcpServers": {
    "arcnautical": {
      "url": "https://mcp.arcnautical.com/mcp",
      "headers": { "Authorization": "Bearer arc_live_…" }
    }
  }
}

Anything with curl — the endpoint is plain JSON-RPC over POST:

curl -s https://mcp.arcnautical.com/mcp -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"check_vessel","arguments":{"imo":"9274446"}}}'

The remote endpoint is a thin client of the same public API: a keyless call counts against your 100-per-hour allowance (the caller's address is forwarded), and a keyed call is metered on your key exactly as a direct API call would be. GET /mcp answers 405 — there is no server-to-client stream to hold — and GET https://mcp.arcnautical.com/health reports the endpoint's version.

Local server (stdio)

Requires Node 18+. No install step — every client below runs it with npx.

Claude Desktop — claude_desktop_config.json:

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

Claude Code

claude mcp add arcnautical -- npx -y @arcnautical/mcp

Cursor / Windsurf / VS Code — same command / args shape in the client's MCP settings.

To unlock the full record, batches and voyage scoring, add an API key to the env block:

{
  "mcpServers": {
    "arcnautical": {
      "command": "npx",
      "args": ["-y", "@arcnautical/mcp"],
      "env": { "ARCNAUTICAL_API_KEY": "arc_live_…" }
    }
  }
}

Keys are free and self-serve at https://arcnautical.com/get-a-key?from=mcp — no card, no approval step. A new key includes a one-time free allowance of vessel screenings and a monthly allowance of voyage assessments; get_usage reports both, and the current numbers are on arcnautical.com/developers.

Tools

Tool	Key?	What it does
check_vessel	no	Sanctions status (OFAC SDN, EU, UN, UK OFSI, OpenSanctions), ownership-opacity score, A–E vetting grade for one IMO. 100/hour per IP.
find_port	no	Resolve a port name or country to UN/LOCODEs — call before score_voyage.
screen_vessel	yes	The full screening record: every match with its source list, programme and confidence class, the graded vetting factors, per-source freshness, a retained record id. Same hull asked again today replays free.
screen_vessels	yes	Batch up to 50 IMOs and wait for the results.
get_screening	yes	Retrieve a stored record by id (retained ten years).
score_voyage	yes	Route risk between two LOCODEs: score, level, drivers, confidence, missing sources.
get_usage	yes	Remaining allowance and limits for the configured key.

Reading a verdict

• RED — confirmed match on the vessel identifier. AMBER — possible match, review it. GREEN — no match against the sources reached. INCOMPLETE — a core source could not be read; never present it as clear.
• coverage_complete: false on a GREEN means one supplementary list was unavailable: re-screen before relying on it.
• assessed: false means ownership and vetting are defaults, not findings.
• The keyless check matches the vessel's current name and identifiers only. A hull renamed after a designation can read GREEN there; screen_vessel covers that case.
• Designations change daily. Quote the checkedAt / screened_at time with any answer.

Idempotency

Every resource-creating call sends an Idempotency-Key derived from the question — the hull and the UTC day — not from the attempt. Asking about the same vessel twice in a day returns the stored record and spends nothing. The API's docs measured 42% of one integration's monthly screenings as same-day repeats billed only because their client generated a random key per call; this server does not do that.

Environment

Variable	Default	Purpose
ARCNAUTICAL_API_KEY	unset	Enables the keyed tools (stdio; the remote endpoint reads the Authorization header instead).
ARCNAUTICAL_BASE_URL	https://arcnautical.com	Override for testing.
PORT / HOST	3005 / all interfaces	--http only.
MCP_TRUST_PROXY	unset	--http only: 1 reads the caller's address from X-Real-IP / CF-Connecting-IP set by a reverse proxy. Only when nothing but the proxy can reach the port.

Self-hosting the HTTP endpoint

npx -y @arcnautical/mcp --http serves POST /mcp on port 3005 — useful when your assistants run in a network that cannot spawn local processes but can reach one internal URL. The Dockerfile in this repository builds the same thing; it is what mcp.arcnautical.com runs.

Links

• Guide: https://arcnautical.com/developers/
• Reference: https://arcnautical.com/developers/reference/
• OpenAPI 3.1: https://arcnautical.com/api/v1/openapi.json
• Postman: https://www.postman.com/arcnautical-6322764/arcnautical-s-workspace
• For agents: https://arcnautical.com/llms.txt
• Listed on: MCP registry (com.arcnautical/mcp) · Smithery · npm · Wellknown (verified owner; live reachability checks)

Development

npm install
npm test        # builds, then drives dist/cli.js over stdio AND createHttpServer() over Streamable HTTP
                # (a local stub API asserts the forwarded caller address and Bearer key; one call hits prod keyless)
npm run start:http   # the remote endpoint on http://localhost:3005/mcp

MIT © ArcNautical