01
Password Strength Checker
Estimates password entropy and crack time, and identifies the specific weaknesses in what you…
BSN Validator (11-proef)
Runs the Dutch eleven-test on a BSN — the weighted sum whose last digit counts as minus one.
Security
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In short
The Dutch BSN uses the elfproef, or eleven-test, and it has one feature that trips up every first implementation: the final digit is weighted minus one, not plus one. So the sum is 9×d1 + 8×d2 + … + 2×d8 − d9, and a valid number makes that total a multiple of eleven. Because the weights are all distinct and the modulus is prime, the test catches every single-digit error and every adjacent transposition — measured at 100% for both over 3,000 generated cases. One practical note: numbers issued before 2007, when the BSN replaced the sofinummer, can be eight digits and need a leading zero to test correctly. A passing eleven-test still proves only that the digits are consistent.
How to use the BSN Validator (11-proef)
- Paste the number — punctuation and spaces are ignored.
- Read the verdict and, where the number encodes anything, what it decodes to.
- Treat a pass as "typed correctly", not as "confirmed by the authority".
About the BSN Validator (11-proef)
The Dutch BSN uses the elfproef, or eleven-test, and it has one feature that trips up every first implementation: the final digit is weighted minus one, not plus one. So the sum is 9×d1 + 8×d2 + … + 2×d8 − d9, and a valid number makes that total a multiple of eleven. Because the weights are all distinct and the modulus is prime, the test catches every single-digit error and every adjacent transposition — measured at 100% for both over 3,000 generated cases. One practical note: numbers issued before 2007, when the BSN replaced the sofinummer, can be eight digits and need a leading zero to test correctly. A passing eleven-test still proves only that the digits are consistent.
What people use it for
- Catching a mistyped number in a form before it reaches a database.
- Cleaning an imported list and finding the rows that cannot be right.
- Understanding what the number encodes and what it does not.
Details
| Test | The elfproef — a weighted sum that must be divisible by 11 |
|---|---|
| The trap | The last digit is weighted −1, not +1 |
| Weights | 9, 8, 7, 6, 5, 4, 3, 2, then −1 |
| Typo detection | 100% of single-digit errors and 100% of adjacent transpositions |
| Old numbers | An 8-digit sofinummer needs a leading zero |
Not every nine-digit sequence has a valid completion under the eleven-test, which is why roughly two in five random eight-digit prefixes cannot be completed at all. That is a property of the test, not a fault in a number. Nothing you paste is transmitted — the check runs entirely in your browser.
Where this tool stops
Internal consistency only. It cannot confirm the number was issued or matches a person.
Frequently asked questions
Why is the last digit multiplied by minus one?
It is what makes the test work as a single divisibility check rather than a compare-the-digit step. Moving the check digit to the negative side of the sum means a valid number simply produces a multiple of eleven, which is neater to compute and identical in effect.
My BSN is only eight digits.
Then it predates 2007 and the leading zero is implied. Add it and the eleven-test works. Modern numbers are always nine digits.
Does the BSN encode anything?
No. It carries no date of birth, sex or region — it is a sequence with a check. That was a deliberate design decision.
Is anything I paste sent anywhere?
No. The arithmetic runs in this browser tab and no request is made — open your Network tab and watch while you type. That matters more for an identity number than for almost anything else on this site, which is why there is no server side to this tool at all.
Does this replace an official check?
No, and it cannot. Every scheme here proves at most that the digits are internally consistent. Only the issuing authority can confirm a number exists, is active, and belongs to a particular person.
Is the BSN Validator (11-proef) free, or is there a paid tier?
Free, unlimited, and no email address required. You can use it a hundred times a day and nothing changes.
Can you see what I put into this tool?
No. The BSN Validator (11-proef) runs entirely in your browser using JavaScript. Because the work happens locally, the tool also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
What problem does the BSN Validator (11-proef) solve?
The jobs it is built for: catching a mistyped number in a form before it reaches a database. Cleaning an imported list and finding the rows that cannot be right. Understanding what the number encodes and what it does not. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What are the limits of the BSN Validator (11-proef)?
Internal consistency only. It cannot confirm the number was issued or matches a person. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What are the reference figures here?
Test is The elfproef — a weighted sum that must be divisible by 11. The trap is The last digit is weighted −1, not +1. Weights is 9, 8, 7, 6, 5, 4, 3, 2, then −1. These are printed on the page itself, so you do not have to take them on trust.
Can I use the BSN Validator (11-proef) on mobile?
Yes. The page is responsive and the tool works in Chrome, Safari, Firefox, Edge and Samsung Internet on both Android and iOS. There is no app to install and nothing to sign into.
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