sheetmask 0.1.2

CLI for creating PII-safe Excel test fixtures

sheetmask

Turn a real Excel file into a safe test fixture — fake names, fake numbers, real structure.

Install

pip install git+https://github.com/daniel-butler/sheetmask.git

uv add git+https://github.com/daniel-butler/sheetmask.git

Quickstart

1. Run analyze on your file. It prints a prompt describing the columns and sample data — copy it.

sheetmask analyze "Q4 Expense Report.xlsx"

2. Paste the prompt into Claude or ChatGPT. Save the config it returns:

# q4_expense_config.py
from sheetmask import PercentageVarianceRule, PreserveRelationshipRule

config = {
    "version": "1.0.0",
    "sheets_to_keep": ["Expenses"],
    "entity_columns": {
        "Employee Name": "PERSON",
        "Department": "ORGANIZATION",
        "Manager": "PERSON",
    },
    "numeric_rules": {
        "Reimbursement": PercentageVarianceRule(variance_pct=0.2),
        "Net Amount": PreserveRelationshipRule(
            formula="context['Reimbursement'] - context['Deduction']",
            dependent_columns=["Reimbursement", "Deduction"],
        ),
    },
    "preserve_columns": ["Date", "Category"],
}

3. Run process. The output lands beside the original.

sheetmask process "Q4 Expense Report.xlsx" --config q4_expense_config.py
# Output: Q4 Expense Report_SYNTHETIC.xlsx

Reference

Entity types

Each unique value maps to the same fake value throughout the file, so relationships between rows stay intact.

Type	Generates
PERSON	Full name
PERSON_FIRST_NAME	First name only
PERSON_LAST_NAME	Last name only
ORGANIZATION	Company name
EMAIL_ADDRESS	Email address
PHONE_NUMBER	Phone number
PROJECT_NAME	Project name
LOCATION	City, State

Numeric rules

PercentageVarianceRule replaces each value with a random number within a band of the original. Use it for independent figures.

"Headcount": PercentageVarianceRule(variance_pct=0.15)
# 100 becomes a random number between 85 and 115.

PreserveRelationshipRule derives a value from other already-anonymized columns. Use it wherever one column is computed from others, so the arithmetic stays consistent.

"Gross Margin": PreserveRelationshipRule(
    formula="context['Revenue'] - context['Cost']",
    dependent_columns=["Revenue", "Cost"],
)
# Gross Margin will always equal anonymized Revenue minus anonymized Cost.

All commands

Command	Description
sheetmask analyze <file>	Analyze file and print LLM prompt
sheetmask analyze <file> -o prompt.txt	Save LLM prompt to a file
sheetmask analyze-multi f1 f2 f3	Analyze multiple files for shared schema patterns
sheetmask process <file> --config config.py	Anonymize file using config
sheetmask process <file> out.xlsx --config config.py --seed 42	Write to named output with fixed random seed