Calendar Converter (Gregorian/Julian/Hebrew/Islamic)
Convert dates between Gregorian, Julian, Hebrew, and Islamic calendars with Julian Day Numbers. Essential for working with historical documents.
Research & Analyze with The Historian's Knife
Calendar systems, numerals, and genealogy tools — offline, forever
You need to research & analyze. Deep research with local AI. The Historian's Knife delivers 5 purpose-built tools in a single HTML file.
The Historian's Knife puts five essential history and genealogy tools into a single HTML file. Convert dates between Gregorian, Julian, Hebrew, and Islamic calendars with Julian Day Numbers, convert Roman numerals in both directions with full reference tables, explore ancient numeral systems including Babylonian, Egyptian, and Mayan, look up regnal years for English and French monarchs, and compute Soundex codes for genealogical name matching — all offline, all private, all yours forever.
WHAT'S INSIDE
5 tools in a single HTML file
Roman Numeral Converter
Convert between Roman numerals and Arabic numbers in both directions. Includes a reference table and handles values up to 3,999,999.
Ancient Numeral Systems
Explore Babylonian sexagesimal, Egyptian hieroglyphic, Mayan vigesimal, and other ancient number systems with interactive conversion.
Regnal Year Calculator
Look up regnal years for English and French monarchs — convert between regnal dates (e.g., '3 Henry VIII') and calendar dates.
HOW IT WORKS
Three steps. No setup.
1
Download the file
Purchase The Historian's Knife and download a single HTML file. No installer, no account, no setup.
2
Open in any browser
Double-click to open in Chrome, Firefox, Safari, or Edge. Works on any operating system.
3
Start working
Your data stays in your browser's local storage. Nothing is uploaded. Ever.
COMPLIANCE & GEOGRAPHY
Global
Works in any country. No server dependency, no regional restrictions.
FAQ
Frequently Asked Questions
How does The Historian's Knife help me research & analyze?
The Historian's Knife provides 5 interconnected tools for deep research with local ai. Calendar converter (Gregorian, Julian, Hebrew, Islamic), Roman numeral converter, ancient numeral systems, regnal year calculator, and genealogy Soundex. Your archive in a file.
Do I need an internet connection to research & analyze with The Historian's Knife?
No. The Historian's Knife runs entirely in your browser as a single HTML file. All 5 tools work offline.
What is the difference between The Historian's Knife and cloud-based alternatives?
Cloud tools store your data on external servers, require subscriptions, and stop working without internet. The Historian's Knife is a one-time purchase ($39) that runs locally. Your data never leaves your device.
Can I use The Historian's Knife on multiple devices?
Yes. Once purchased, you can use The Historian's Knife on any device with a web browser. Copy the HTML file to as many devices as you need.
No cloud One fileOne-time purchase
Get The Historian's Knife — $39Sovereignty as a Service