Welcome to Chris Spackman's NeoCities page

I loved GeoCities back in Japan in the 1990s, so was thrilled to discover NeoCities. I'm using this site mostly for educational tools and JavaScript experiments that I make for my schools and classes, and for other teachers and students.

Everything here is free to use. Please don't hesitate to email me at chris@chrisspackman.com with bug reports, suggestions for improvements, or requests for other teacher-tool pages.

News

2026-07-13: Added another game — neojongg, a mahjongg solitaire in plain HTML/CSS/JS. Every board is guaranteed solvable, and the Daily game is the same for everyone, so you can compare times with friends.

2026-07-09: Added a game I have been working on for a while — 2076: Sengoku America is a game of legitimacy, influence, and war across a fractured USA. The game is currently at version 0.9 beta 1. Feedback and suggestions most welcome.

2026-07-03: Added a Word Games and Puzzles section. Currently has generators for Bingo, Word Searches and Crossword, and Word Scramble puzzles.

Several tweaks and bug fixes in the cryptography and crypanalysis pages.

2026-06-24: Added Sentence Creator, a tool to help reading teachers come up with sentences based on the sounds and letters that they have taught their students.

K–12 Supports

Browser-based tools for teachers and students — especially for reading, phonics, and English Learner support. They run entirely in your browser, with nothing to install.

Cryptography & Code-Breaking

Interactive demos that explain how ciphers work — and how they get broken — from pen-and-paper classics to the math behind modern key exchange.

Traditional Cryptography Seven classic pen-and-paper ciphers, from trivially breakable to unbreakable. Early Modern Cryptanalysis Codebooks, the Zimmermann Telegram, the Black Chamber, and Friedman's methods. Cryptanalysis: Breaking Ciphers Hands-on tools for breaking substitution, Vigenère, and transposition ciphers. CODEX Codebook Suite Build, use, and break codebook ciphers with an encoder, a maker, and a decryptor. Simplified Diffie-Hellman How two people create a shared secret over an insecure channel. Public/Private Key Generation The math behind creating a public and private key pair.

Command Line & Computing

Point-and-click helpers for some powerful but fiddly tools.

commandCraft GUIs that build commands for ten CLI tools (curl, ffmpeg, find, GPG, rsync, and more).

Math & Probability

Coin-Flip Probability "Flip" any number of coins and watch the law of large numbers at work.

Just for Fun

2076: Sengoku America A game of legitimacy, influence, and war across a fractured USA. (Currently version 0.9 beta 1) neojongg A mahjongg solitaire game. Every board is guaranteed solvable, and the Daily game is the same for everyone. Fortune An online version of the classic BSD / Linux fortune program. Age Verification A proof-of-concept: can you prove your age using historical knowledge?

Reference

Glossary of Terms Plain-English definitions of the math, cryptography, and probability terms used across these tools.

My Other Sites

ChrisSpackman.com — my more professional documents and information.
OsugiSakae.com — my personal and older stuff. May I suggest Mandated Reporter: My Conversations with Nnedi, a short story set in the near future, dealing with GenAI agents in education.
OpenHistory.org — my site for Free / Open content on Japanese History. I started it about 25 years ago and have not updated it in a (very) long while. That will change soon, now that I've switched it back to LaTeX.

Disclaimer: these pages are educational demos provided as-is, with no warranty of any kind. The author is not responsible for any consequences arising from their use.

Send comments and bug reports to chris@chrisspackman.com.

Last updated: 2026-07-13

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.