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 Essential for working with historical documents.
The Historian's Knife for Researcher / Academics
Calendar systems, numerals, and genealogy tools — offline, forever
Deep research without surveillance. The Historian's Knife gives researcher / academics 5 specialised tools in a single HTML file that runs entirely offline.
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
Why should Researcher / Academics use The Historian's Knife?
The Historian's Knife is built for researcher / academics who need the weird & wonderful tools without cloud dependencies. Calendar converter (Gregorian, Julian, Hebrew, Islamic), Roman numeral converter, ancient numeral systems, regnal year calculator, and genealogy Soundex. Your archive in a file.
Does The Historian's Knife work offline?
Yes. The Historian's Knife is a single HTML file that runs entirely in your browser. No internet connection required. Your data never leaves your machine.
Is The Historian's Knife a subscription?
No. The Historian's Knife is a one-time purchase ($39). No monthly fees, no renewals, no price increases.
What tools are included in The Historian's Knife?
The Historian's Knife includes 5 tools: Calendar Converter (Gregorian/Julian/Hebrew/Islamic), Roman Numeral Converter, Ancient Numeral Systems, Regnal Year Calculator, Genealogy Soundex. All accessible from a single HTML file.
Can I try The Historian's Knife before buying?
Yes. Every product page includes an interactive demo you can try in your browser. No signup required.
No cloud One fileOne-time purchase
Get The Historian's Knife — $39Sovereignty as a Service