Vessel Check API

Screen a ship by IMO number for sanctions, ownership opacity and a vetting grade. The first call needs no key and no signup.

curl https://arcnautical.com/api/v1/vessels/9034690/check

The response, abridged (live on 2026-10-10):

{
  "imo": "9034690",
  "vesselName": "LUMA",
  "checkDigitValid": true,
  "sanctions": {
    "status": "RED",
    "detail": "2 confirmed matches on vessel identifier.",
    "coverageComplete": true,
    "coverageGaps": []
  },
  "ownership": { "opacity": "HIGH", "score": 100 },
  "ownershipFactors": [
    { "label": "Owner not identified, so no LEI (GLEIF) lookup was possible", "points": 35 },
    { "label": "Flag jurisdiction VU — Tier 3 — Opaque", "points": 25 },
    { "label": "No public beneficial-ownership record on a flag-of-convenience register", "points": 10 },
    { "label": "OFAC-designated entity in ownership chain (chain-sanctions floor applied)", "points": 30 }
  ],
  "vetting": { "grade": "E", "score": 90, "status": "unacceptable" },
  "assessed": true,
  "checkedAt": "2026-10-10T18:45:05.318Z",
  "fullReport": "https://arcnautical.com/check?imo=9034690",
  "tier": "keyless"
}

The full API reference is at arcnautical.com/developers. The OpenAPI 3.1 spec is at /api/v1/openapi.json.

What one call checks

• Sanctions. Five lists: OFAC SDN, UK OFSI, EU Financial Sanctions (FSD), the UN Security Council Consolidated List, and OpenSanctions' maritime dataset. The hull is matched on its IMO number, its current name and the other names our sources hold for it. A former name that none of our sources holds is not screened, so a ship renamed after a designation under a name we never saw can still read GREEN.
• Ownership opacity. A 0-100 score for how much of the ownership is on the public record: whether the owner has a GLEIF LEI, how transparent the flag register is, and whether a designated company sits in the chain. ownershipFactors lists the lines the score is the sum of.
• Vetting grade. A to E, a composite of five factors: detention history, flag performance, vessel age, inspection gap and ownership opacity. Detention and inspection history comes from port state control records. Which regimes we cover, and the gaps, are listed in the methodology.

Response fields

Field	Type	Meaning
imo	string	The seven-digit IMO that was screened
vesselName	string | null	The name our sources hold for this hull, so you can confirm which ship was screened. null when no source names it
alsoRecordedAs	array	Other names our sources hold for the hull, each with its source. Every one was screened on this call
identityBasis	sources | user | none	sources means our records name the hull. none means nothing named it: its identifiers were screened, a name was not
checkDigitValid	boolean	false when the IMO fails its check digit. That is almost always a typo
sanctions.status	RED | AMBER | INCOMPLETE | GREEN	See below
sanctions.detail	string	The verdict in a sentence
sanctions.coverageComplete	boolean	true when every sanctions list loaded
sanctions.coverageGaps	string[]	The lists that did not load
ownership.opacity	LOW | MEDIUM | HIGH | null	Opacity band
ownership.score	number | null	0 = transparent, 100 = opaque
ownershipFactors	array | null	The lines ownership.score is the sum of, with their points. Labels are for people to read, not codes to parse
vetting.grade	A-E | null	Vetting grade
vetting.score	number | null	0-100, lower is better
vetting.status	string	acceptable, marginal, substandard, unacceptable, or not_assessed
assessed	boolean	false means ownership and vetting were not measured: their values are null, with no stand-in. The sanctions verdict is unaffected
checkedAt	ISO 8601	When the check ran
fullReport	URL	The human-readable report for this hull
tier / tierDetail	string	Always keyless here, and what a free key adds

Sanctions status

Status	Meaning
RED	Confirmed match. Do not proceed without legal review
AMBER	Possible match that needs a person to review it
INCOMPLETE	No match, but the screen cannot be called clear. A core list (OFAC SDN, OpenSanctions, EU FSD) did not load, or no source could name the hull, or the IMO fails its check digit. detail says which. Never treat it as clear. It is never cached, so a retry gets a fresh screen
GREEN	No match on the lists that loaded. If coverageComplete is false, one supplementary list was unavailable: re-screen rather than treat it as a clean pass

Ownership opacity

Band	Score
LOW	0-30
MEDIUM	31-60
HIGH	61-100

Opacity measures the public record, not wrongdoing. Ordinary tonnage on an open register can score HIGH simply because the owner has no LEI. Read ownershipFactors to see why.

Vetting grade

Grade	Score	vetting.status
A	0-20	acceptable
B	21-40	acceptable
C	41-60	marginal
D	61-80	substandard
E	81-100	unacceptable

Limits

• 100 requests an hour per IP address. The X-RateLimit-Limit, X-RateLimit-Remaining and X-RateLimit-Reset headers on every response are the authority. The window slides, so X-RateLimit-Reset is when your oldest request ages out.
• A refused request gets 429 with Retry-After. A tight loop is refused before the hourly allowance is spent. Honor Retry-After and the loop completes.
• A hull anyone checked in the last hour answers from cache. A hull that needs a fresh screen waits for one of a few screening slots shared by every keyless caller. If none frees up in time you get 503 keyless_busy with Retry-After, and it does not count against your allowance.
• An IMO without exactly one seven-digit number in it gets 400 invalid_imo, which does not count either. 9811000 and IMO9811000 both work.
• The keyless check is a sample for evaluation and occasional lookups, not a data feed. An automated client that runs a product on it can be held to a small monthly sample. The refusal names the free key that replaces it.

Every limit and error code is documented at arcnautical.com/developers.

With a free key

A self-serve API key is free, with no card. POST /api/v1/screenings runs the same engine and returns the full record the keyless check leaves out: every sanctions match with its list, programme and confidence class, each source reported separately, the five weighted vetting factors, and a stored screening record you can cite later. The same key does batches of 50, standing monitors, fleets, signed webhooks and voyage risk scoring.

Get one at arcnautical.com/get-a-key.

Examples

Python

import requests

r = requests.get("https://arcnautical.com/api/v1/vessels/9034690/check", timeout=30)
if r.status_code == 429:
    raise SystemExit(f"Rate limited, retry in {r.headers.get('Retry-After')} s")
r.raise_for_status()
v = r.json()

status = v["sanctions"]["status"]
if status in ("RED", "AMBER"):
    print(f"Review IMO {v['imo']} ({v['vesselName']}): {v['sanctions']['detail']}")
elif status == "INCOMPLETE":
    print(f"Not a clearance: {v['sanctions']['detail']}")
elif not v["sanctions"]["coverageComplete"]:
    print(f"Clear on the lists that loaded; missing {v['sanctions']['coverageGaps']}. Re-screen.")
else:
    print(f"No match for IMO {v['imo']} ({v['vesselName']})")

JavaScript

const res = await fetch("https://arcnautical.com/api/v1/vessels/9034690/check");
const v = await res.json();

console.log(`Sanctions: ${v.sanctions.status}`);
if (v.assessed) {
  console.log(`Ownership opacity: ${v.ownership.opacity} (${v.ownership.score}/100)`);
  console.log(`Vetting grade: ${v.vetting.grade} (${v.vetting.status})`);
} else {
  console.log("Ownership and vetting: not assessed");
}

cURL

curl -s https://arcnautical.com/api/v1/vessels/9811000/check | jq '{imo, vesselName, sanctions: .sanctions.status, grade: .vetting.grade}'

# A few hulls, one after another
for imo in 9034690 9811000 9703318; do
  curl -s "https://arcnautical.com/api/v1/vessels/$imo/check" | jq -c '{imo, vesselName, sanctions: .sanctions.status}'
  sleep 1
done

Google Sheets (Apps Script)

function VESSEL_SANCTIONS(imo) {
  const res = UrlFetchApp.fetch(`https://arcnautical.com/api/v1/vessels/${imo}/check`);
  return JSON.parse(res.getContentText()).sanctions.status; // RED, AMBER, INCOMPLETE or GREEN
}

From an AI agent (MCP)

The same check is an MCP tool. Add the remote endpoint https://mcp.arcnautical.com/mcp with no authentication and check_vessel and find_port work at once. To run it locally instead: npx -y @arcnautical/mcp. Setup for Claude, ChatGPT, Cursor and others: arcnautical.com/developers/#mcp.

Try these

IMO	Vessel	What you will see
9034690	LUMA	RED: confirmed matches on the vessel identifier
9811000	EVER GIVEN	GREEN, grade A, opacity HIGH (70): a clean ship whose ownership is not on the public record
9703318	MSC ZOE	GREEN, grade A
9295345	none	INCOMPLETE: the number fails its IMO check digit, so it belongs to no vessel

These were the answers on 2026-10-10. Verdicts change when the lists change.

Data

Sanctions lists from the US Treasury (OFAC), HM Treasury (OFSI), the European Union, the UN Security Council and OpenSanctions. Ownership data from GLEIF. Port state control records from the MoU regimes named in the methodology.

Use of the API is covered by the terms of service. Questions: admin@arcnautical.com.

Built by ArcNautical.