Resident Number Masker
Finds resident numbers in text or a spreadsheet column and masks them to the legally acceptable form.
Attaching a document to an application usually means the resident numbers in it have to be masked first, and doing that by hand across a spreadsheet is where one gets missed. This finds them by pattern and replaces the part that has to go.
Document
Paste a whole document and only the resident numbers in it are masked.
How much to hide
900101-1****** — the minimum the 개인정보보호법 (Personal Information Protection Act) requires.
Result
Numbers masked
2
See what changed
- 900101-1234568 900101-1******
- 850101-5234567 850101-5******
Only 13-digit runs whose first six are a real date are masked. An order number or an account number that happens to be 13 digits is left alone — a tool that damages unrelated data does not get used on a real document twice. In the other direction, a number issued after October 2020 whose check digit does not match is masked all the same.
There is no function here that generates a 주민등록번호.
Validating and masking have uses. A function that manufactures a structurally valid number has exactly one — getting past an identity check. And a “structurally valid” number is usually a number that belongs to a real person. So it is not built.
What you type is handled inside this tab and is not transmitted anywhere.
How to use it
Paste the text or the table
Numbers are found wherever they appear, including inside a sentence, with or without the hyphen.
Check the count before you accept it
The number of matches is shown. If it is lower than you expected, something in the document is formatted differently — a full-width digit, a number split across two cells, a space in the middle.
Read the masked output once
Masking is not redaction of the surrounding text. A name, an address and a phone number next to a masked number still identify the person.
Common questions
How much has to be masked?
The common requirement is that the digits after the first of the second block are hidden — the birth date and the century digit stay. Which form a particular recipient accepts is their rule, so check what they asked for before sending.
Can it mask a PDF or an image?
Not here — this works on text you paste. For a PDF, the redaction tool removes the content rather than covering it; a black rectangle drawn over a PDF leaves the text underneath selectable.
Is the document uploaded?
No. It is processed in the browser. A tool for handling personal data that sent the data somewhere would be self-defeating.
Feed it from
PDF Redactor
Deletes the underlying text and image content inside marked areas, not just a black rectangle on top.
Text Anonymiser
Finds emails, phone numbers, card numbers and IDs in free text and masks or pseudonymises them.
Resident Number Format Validator
Checks whether a 13-digit resident number is structurally valid — date part, region rules and check digit.
Business Registration Number Validator
Checks the 10-digit check sum of a Korean business number and can bulk-validate a pasted column.
Next
These accept what this tool produces, so the result can go straight in.
CSV Cleaner
Trims cells, normalises headers, fixes number and date formats and reports rows with the wrong column count.
Resident Number Format Validator
Checks whether a 13-digit resident number is structurally valid — date part, region rules and check digit.
PDF Redactor
Deletes the underlying text and image content inside marked areas, not just a black rectangle on top.
Text Anonymiser
Finds emails, phone numbers, card numbers and IDs in free text and masks or pseudonymises them.
Korean Age Calculator
Works out your 만나이, 연나이 and the old 세는나이 from a birth date, on any reference day.
Annual Leave Calculator
Works out how many paid leave days have accrued by joining date or fiscal year, including the first-year rule.