Container number check (ISO 6346)
A container number is four letters and seven digits, and the last digit is a check digit computed from the first ten characters. That makes a mistyped number provable: the check digit will not match. This validator uses the same engine as the paid product.
Check a container number
Every container number ends in a check digit computed from its first ten characters. A typo anywhere — owner code, letter, digit — changes that digit, which is how a wrong container number becomes provable instead of arguable.
How the check digit works
- 1. Each letter maps to a value between 10 and 38, skipping multiples of 11.
- 2. Each of the first ten positions carries a weight: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512.
- 3. Multiply, sum, take the remainder modulo 11, then that remainder modulo 10.
- 4. The result must equal the eleventh character.
If the number is malformed we say so instead of guessing, and if it is well-formed but the check digit disagrees we show both digits so the disagreement can be traced to the exact character.
When a wrong container number matters
A container number that does not match the booking causes gate-in rejections, mis-routed releases and reworked manifests. On a Bill of Lading it is one of the defects the full checker reports alongside weight, unit, date and Incoterm problems.
Check a whole Bill of LadingQuestions
- Does this cost anything?
- No. The container validator never consumes quota, signed in or not.
- Is the number sent anywhere?
- It is checked on this deployment. Nothing is written to disk and nothing is stored beyond the anonymous quota counter.
- Can I use it from code?
- Yes: POST /api/v1/check-container with {"number":"CSQU3054383"}. See the API documentation.