# Data Anonymizer

Anonymize personal data in Excel (.xlsx) and CSV files, one column at a time. Mask names, keep only the domain of e-mail addresses, or give the same person the same alias. Check the before and after tables and the count per column, then save. The tool guesses personal-data columns from their headers and values and sets a first method.

- URL: https://tools.itlibra.com/en/data-anonymizer
- On-device・No upload
- Last updated: 2026-10-23

## How to use

1. Drop an Excel (.xlsx) or CSV / TSV file, or click “Choose files”. “Try a sample” creates a practice customer list.
2. Under “Method per column”, check the guess and method for each column. Change the methods that are wrong, and set “Keep as is” for columns that can stay.
3. Choose how many characters to keep, the mask character, and whether repeated values get the same alias.
4. In the “After” table, check the yellow cells (changed) and the count for each column.
5. Choose the format (Excel / CSV) and encoding, then download. Before you share the file, check whether the columns you kept can identify a person together.

## Use cases

- Mask names and phone numbers before a customer list goes to an internal test
- Keep the same respondent linked across a survey by an alias such as “Customer0001” and pass it on for analysis
- Build a test table by masking the address completely and rounding birth dates to decades
- Keep only the last 4 digits of card numbers for matching support requests
- Round sales figures to ranges of 100 to hide exact amounts

## What it does

### Column guesses to start from

The tool guesses personal-data columns from their names (name, e-mail, phone and so on) and their values, and sets a first method. It also reads full-width digits, postal codes without hyphens, and card numbers that pass the Luhn check.

### Same value, same alias

Within a column, a repeated value always becomes the same alias such as “Customer0001”. The same person stays linked across rows, which helps analysis and testing.

### Masking, domain kept, hashing

Mask with the number of characters you keep and the mask character, keep only the part of an e-mail address from @ on, or hash with SHA-256 keyed by a secret made only in this page.

### Check before you save

Changed cells are yellow, and each column shows how many cells it changed. Save as Excel (.xlsx) or CSV, and choose the text encoding.

### Processed only in your browser

Reading, anonymizing and building the download all happen on your device, and no data is sent. The hash secret is not stored, and it changes when the page is reloaded.


## Supported formats

### Input

- Excel (.xlsx / .xlsm)
- CSV (.csv)
- TSV (.tsv / .txt)

### Output

- Excel (.xlsx)
- CSV (UTF-8 with BOM / UTF-8 / Shift\_JIS / EUC-JP / UTF-16)


## Capability matrix

| Feature | Support | Notes |
| --- | --- | --- |
| Guessing name, e-mail, phone, postal code, address, birth date and card number columns | Supported | From the header and values; guesses can be wrong |
| Masking (choose the characters kept at the start and end, and the mask) | Supported | — |
| Keep only the e-mail domain (the part from @ on) | Supported | — |
| Same value, same alias (consistent within a column) | Supported | Aliases are numbered in order of appearance |
| Hash (SHA-256 with a secret made only in this page) | Supported | Only for this session; values change on reload |
| Dates as year and month or decade, numbers as ranges, removing a column | Supported | — |
| Finding personal data inside free text (the body of a memo column) | Not supported | Methods are chosen per column |
| Judging whether a combination of columns identifies a person | Not supported | Not judged |
| Several sheets in one run | Partial | One sheet at a time. Only the processed sheet is saved, so other sheets never go out with their original values |
| Keeping formulas, formatting and merged cells | Not supported | Only values are saved |
| Legacy Excel (.xls) | Not supported | Re-save as .xlsx in Excel first |

## Limits & notes

- Works on smartphones too, but with many columns, setting each one takes time, so a PC is more comfortable.
- Up to 100 MB per file.
- Characters kept at the start and at the end are 0–10 each. Range widths are 10, 100, 1000 or 10000.
- When the characters kept cover the whole value, that value is masked completely.
- The hash secret changes when the page is closed or reloaded, so it cannot match values later.
- This is not a guarantee of anonymity. A combination of other columns can still identify a person.

## Privacy & safety

Reading, anonymizing and building the download all happen in your browser. Your data is never sent to or stored on a server. The hash secret stays in the page and is not stored.

## FAQ

### How do I mask personal data in an Excel file?

Open the file, set the name column to “Mask”, and choose how many characters to keep (for example the first 1) and the mask character. Check the “After” table before you save.

### Can I anonymize names and phone numbers in a CSV file at once?

Yes. Each column has its own method, so you can mask names and keep only the last 4 digits of phone numbers in one pass. You can save as CSV (UTF-8 and others) or as Excel.

### How do I hide only the part before @ in an e-mail address?

Set the method to “Keep only the domain of e-mail”. The part before @ is masked and the domain stays. A value that is not in the form name@domain is masked completely.

### Can I keep the same person under the same alias?

Yes. With “Same value, same alias”, a repeated value in a column becomes the same alias such as “Customer0001”. Numbers are given in order of appearance.

### Does anonymizing make a person impossible to identify?

No guarantee is given. Other columns, such as birth date and address together, can still identify a person, so check the whole table before you share it.

### Is my data uploaded?

No. Everything runs in your browser, and your data never leaves your device.