Excel Data Masking & Restore Tool Mask confidential columns before sharing with AI, restore with one click

What is Excel Data Masking & Restore Tool?

Before sharing Excel files with ChatGPT, Claude, Gemini or other AI tools, replace sensitive data like names, phone numbers, ID numbers, customer names, and amounts with codes. After AI processing, restore everything with one click using a mapping table. All processing happens locally in your browser—no files are uploaded.

Three-Step Usage

1. Mask: Select a .xlsx file, specify which row is the column header (or which column is the row header), then check which columns or rows to mask. You can also click individual cells directly in the preview. Click "Run Masking" to download the masked Excel and mapping table.
2. Share with AI: Give the AI or colleague only the masked Excel file. Sensitive information is now replaced with codes like S1_CB_001.
3. Restore: In the "Restore" tab, select the processed Excel and mapping table. The tool verifies every cell before making changes, then downloads the restored file.

Masking Rules

• Restorable: Text, numbers, dates, and formulas are replaced with codes. Original values are saved in the mapping table. Identical values in the same sheet and column (or row) use the same code, so AI can still group and calculate statistics.
• Non-restorable: Replaced with "#", not added to mapping. Cannot be restored later. Use for data you don't need to keep.
• Blank cells are not processed. Merged cells are handled as the top-left cell only.

Reuse Codes Across Files

In "Apply Existing Mapping", load File A's mapping and File B to make both Excel files use the same codes for the same customers or items. This helps AI compare across files. The tool uses substring matching with longer terms taking precedence, and creates a new mapping for File B that can be applied to File C as well.

Mapping Tables Can Be Encrypted

When downloading the mapping, set a password to encrypt it as an AES-256 encrypted .zip file. Enter the password when loading it. Mapping tables contain sensitive data—never share them with the masked Excel file and always keep backups. Lost passwords mean lost data.

Notes and Limitations

• Only .xlsx is supported. Convert .xls and .xlsb to .xlsx using Excel first.
• Output preserves cell formatting, but charts, pivot tables, macros, and other advanced objects may not be preserved. Keep your original file.
• If you sort, move cells, or change codes before restoring, the tool will stop and list mismatches to prevent data corruption.

Further Reading

Data masking and pseudonymization are common methods to reduce personal data breach risk. Learn more at Data masking - Wikipedia, Pseudonymization - Wikipedia, and GDPR.