THACO

aka [T] o [H] it [A] rmor [C] lass [Z] ero

An Owlbear.Rodeo extension for calculating your THAC0.

Install in Owlbear Rodeo

1. In Owlbear Rodeo, open your profile menu and choose Add Custom Extension.

2. Paste this manifest URL:

   https://jessescott.github.io/thaco/manifest.json
   

3. Open a scene and click the THACO d20 icon in the toolbar.

If the popover looks stale or blank after an update, hard reload the page (Ctrl+Shift+R).

Features

• Enter your THAC0, the target's Armor Class and your attack bonus to get the d20 roll you need (clamped to 1-20).
• Roll a d20 and see whether it hits or misses. A natural 20 always hits and a natural 1 always misses. Results are shown as an Owlbear notification.
• "Calculate Hit AC" mode: enter (or roll) a d20 and see which Armor Class it hits.
• Named profiles (e.g. "Longsword", "Unarmed") you can add, rename, switch between and delete from the collapsible Profile row.
• Everything is remembered between sessions in the browser, including whether the Profile row is open.
• The popover resizes itself to fit the calculator.

Development

The app lives in THACO/ and is built with Vite and the Owlbear SDK.

cd THACO
npm install
npm run dev        # dev server on http://localhost:5173
npm test           # unit tests (node:test)
npm run test:ui    # Playwright UI tests (run `npx playwright install chromium` once)
npm run build      # production build in dist/

Outside Owlbear the page works standalone; Owlbear-specific calls (notifications) are skipped.

To try a local build inside Owlbear, run npm run dev and add http://localhost:5173/manifest.json as a custom extension.

CI and deployment

• Build and Test installs dependencies, builds, and runs the unit tests and UI tests on every push and PR to main. Node comes from .node-version.
• On a push to main (or a manual run), once those pass, its deploy job publishes THACO/dist to GitHub Pages. Pages must be set to the GitHub Actions source in the repository settings.
• Dependabot opens weekly PRs for npm packages and GitHub Actions.

License

See LICENSE.