The modern way to learn and enjoy Morse code (CW).
A fast, beautiful, sound-first trainer — in the spirit of Monkeytype, Duolingo, and osu!.
Most Morse software still feels like it's from 2004: see a chart of dots and dashes, then translate in your head. That habit hard-caps you around 10 WPM forever. ditdah takes the opposite bet — you learn the way operators actually copy: by sound, one character at a time, with instant feedback and game feel.
The character is never shown as dots and dashes while you decode. You hear it, you type it. That single rule is the whole product.
No sign-up, works offline, installable. Turn your sound on and press Start.
Seven practice modes, all built on one sound-first copy loop:
| Mode | What you copy |
|---|---|
| Learn | Single letters, introduced one at a time (Koch method) |
| Copy groups | Random 5-char groups from your unlocked set |
| Numbers | Digit drills |
| Words | Real English words |
| Callsigns | Realistic ham callsigns (G4ABC, VK2XYZ, W1AW) |
| Free training | Your own character set — with a "weak spots" auto-picker |
| QSO → Story | Realistic on-air exchanges, growing into a narrative campaign |
Plus the things that make it stick:
- Koch + Farnsworth timing — full-speed characters, stretched gaps, so beginners get room without slowing the sound.
- Instant feedback + cues — click-free Web Audio sidetone, a bell on correct, a low tone on a miss.
- Progress that lasts — daily streak, daily goal, rounds with summaries, session history, per-character accuracy.
- Optional cloud sync — sign in (magic link) to back up and sync across devices. Anonymous & local-first by default.
- Yours to tune — character/overall WPM, sidetone, volume, strict mode, an opt-in dit/dah reference (default off).
- Everywhere — keyboard on desktop, on-screen keypad on mobile; installable PWA, fully offline.
- Bilingual UI — English and 简体中文, switchable in-app.
ditdah is developed by a licensed ham + a couple of AI coding agents, coordinating entirely through the repo (issues, PRs, frozen contracts, single-writer status files). That's why the codebase is unusually modular and easy to join — see docs/AGENTS.md.
New contributors are very welcome. The architecture is contracts-first: each module
exposes a frozen types.ts, so you can own a piece without stepping on anyone else.
core/morse Character table, Koch order, Farnsworth timing math (pure)
core/audio Web Audio sidetone scheduler + UI cues (pure logic + thin glue)
core/trainer Session logic: prompts, scoring, unlocks (pure, deterministic)
core/storage Local-first persistence (async, versioned)
app/* Browser glue: settings, progress, history, sync, modes, prompt pools
ui/* React components + the practice loop state machine
content/* Story chapters + prompt content (write chapters, no engine code!)
i18n/* Message catalogs (en + zh) — add a locale = add a file
Great first contributions: add words to the word list, write a Story chapter (pure
content), add a UI translation, or grab a good first issue.
Read CONTRIBUTING.md first — especially the one hard product rule. Then ARCHITECTURE.md for the why, and ROADMAP.md for where it's headed.
npm install
npm run dev # dev server → http://localhost:5173
npm test # unit tests (Vitest)
npm run typecheck # tsc, no emit
npm run lint # oxlint
npm run build # production buildEvery PR must pass typecheck · test · lint · build. Push to main auto-deploys to
GitHub Pages.
React 19 · TypeScript (strict) · Vite · Tailwind v4 · Motion · Vitest · vite-plugin-pwa · Supabase (optional sync). Web Audio API for sample-accurate CW sidetone; local-first persistence.
MIT — free to use, learn from, and build on.