MMSI & IMO maritime identifier decoder
Decode any 9-digit MMSI or 7-digit IMO number entirely in your browser. The decoder bundles 291 ITU-allocated MIDs covering every flag state. For IMO numbers it validates the check digit using the standard 7-6-5-4-3-2 weighting algorithm.
For OSINT investigations: a vessel's IMO number is the most stable identifier — it stays with the hull through name changes, owner changes, and re-flagging. Combine the decoded flag state with the linked external services (MarineTraffic, VesselFinder, Equasis) for current position and history. Cross-check against OpenSanctions for sanctions-listed vessels.
For aircraft equivalents see the ICAO Hex Decoder and Aircraft Enrichment.
Frequently asked questions
What's the difference between MMSI and IMO?
MMSI (Maritime Mobile Service Identity) is a 9-digit ITU-assigned radio identifier transmitted by every AIS-equipped vessel. It changes when a vessel re-flags. IMO (International Maritime Organization) numbers are 7-digit hull identifiers that stay with the physical ship for life — used for sanctions tracking, port state inspections, casualty reporting.
How do you read the country from an MMSI?
The first three digits of a standard ship MMSI form the MID (Maritime Identification Digit) — an ITU-allocated country code. For example, 232–235 = United Kingdom, 211 = Germany, 366–369 = United States. Coast stations, group calls, AtoN, and emergency devices use special prefixes (00, 0, 111, 970, 972, 974, 98, 99) followed by a MID.
How does the IMO check digit work?
For a 7-digit IMO ABCDEFG: multiply A×7 + B×6 + C×5 + D×4 + E×3 + F×2, take the result mod 10. That should equal G. A mismatch means a typo, OCR error, or — concerning — a fabricated number.
Can I look up the actual vessel name from MMSI/IMO?
Not from this page directly — vessel name lookup requires querying an AIS database. Use the linked external services (MarineTraffic, VesselFinder, AISHub) for current name; for historical name changes use Equasis (free, login required) or commercial services. The IMO number is the canonical identifier for cross-database joins.
Why does sanctions matter for shipping?
Many sanctions enforcement programs target vessels by IMO number — Russia/DPRK shadow fleets, Iranian oil tankers, etc. The OpenSanctions search supports vessel queries by IMO. The link above takes you straight there.