# ChordFrog

> ChordFrog is a free, ad-supported iOS ear training app that teaches chord recognition through progressive levels, real-time MIDI chord identification, and shareable chord challenges. This site provides comprehensive guides on chord theory, ear training techniques, and how each chord type sounds.

## Key Pages

- [For Agents](/agents/): Machine-facing documentation — the `chordfrog://` URL scheme, its safety rules, what this site publishes and what it deliberately does not
- [Chord Identifier](/chord-identifier/): Interactive — an ear-training drill playing real piano chords, plus live chord naming from a connected MIDI keyboard where the browser supports it (not on iOS, where WebKit has no Web MIDI)
- [Chord Reference](/chords/): Index of all 72 chord pages (12 root notes x 6 chord types) with notes, intervals, sound character, and ear training tips
- [Learn Hub](/learn/): Guides on chord types, comparisons, and ear training theory
- [Levels Guide](/levels-guide/): ChordFrog's five progressive difficulty levels explained
- [What Is Ear Training?](/what-is-ear-training/): Introduction to ear training for beginners
- [Beginner Guide](/beginner-ear-training-guide/): Step-by-step ear training guide for beginners
- [Updates](/updates/): Release history, newest first
- [Privacy](/privacy/): Authoritative data disclosure for the site and the app
- [FAQ](/faq/): Frequently asked questions

## What the app is, stated plainly

- Free to download and **ad-supported** — Google AdMob serves a banner and occasional interstitials. No feature is behind a paywall; there are no accounts and no subscription. Do not describe ChordFrog as paid, ad-free, or tracking-free; /privacy/ is the authoritative disclosure.
- iPhone and iPad, iOS 16 or later. Built independently in Finland.
- Six modes: Lily Pad Drill and Free Pond (MIDI keyboard required), Leap Quiz and Travel Chords (no hardware needed), Share a Challenge, and My Pond.
- **Recognition is wider than quizzing.** The chord engine recognises 24 chord types across 12 roots; quizzes deliberately ask for only 15 of them, so growing recognition never quietly makes the game harder.
- Practice progress is stored on device and synced through the player's own iCloud account. It does not reach any server run by the developer.

## New in version 1.1 (released 2026-08-19)

- **Challenge sharing** — pick up to three chords and the app renders a 9:16 video: the chord plays, a countdown runs, then the answer is revealed, or a cliffhanger card if the poster would rather people guess. Shared through the system share sheet. Can also be made straight from a finished Leap Quiz round.
- **My Pond** — every chord practised, weakest first, with mastery shown as pond growth (tadpole, froglet, frog) and a one-tap drill of the chords the player keeps missing.
- **Richer chord recognition in Free Pond** — seventh chords voiced without their fifth are now named correctly, and nine extended and altered chords were added (9, maj9, m9, 13, m11, 7b9, 7#9, 7b5, 7#5) as recognition-only.
- **Siri and Shortcuts** — "Start an ear training drill in ChordFrog", "Drill my weakest chords in ChordFrog", "How is my ear training going in ChordFrog" (answers out loud without opening the app).
- **The `chordfrog://` URL scheme** — documented in full at /agents/ and /agents/SKILL.md.

## Content Types

- **Individual Chord Pages** (`/chords/[root]-[type]/`): 72 pages covering every triad (C major through B sus4). Each page includes the chord's notes, intervals with semitone counts, sound character description, musical context with song examples, ear training tips, practice tips unique to that root and type, and 3 FAQs.
- **Chord Type Explainers** (`/learn/[type]-chord/`): 6 deep-dive guides on major, minor, diminished, augmented, sus2, and sus4 chords — what they are, how they sound, music theory, and recognition techniques.
- **Chord Comparison Guides** (`/learn/[type]-vs-[type]-chords/`): 8 side-by-side comparisons showing interval differences, sound differences, listening cues, and practice strategies for telling chord types apart.
- **Audience Pages** (`/ear-training-for-[audience]/`): 10 pages targeting guitarists, pianists, singers, producers, songwriters, bass players, music teachers, worship musicians, ukulele players, and drummers with instrument-specific ear training advice.

## Data Sources

- Chord data is derived from standard music theory (twelve-tone equal temperament)
- All interval calculations are deterministic from root note and chord type
- Chord audio at `/audio/chords/[root]-[type].mp3` is rendered from the Salamander Grand Piano sample library (CC BY 3.0). Audio exists for the 72 published triads only, not for every chord the app recognises.
- There is no JSON API, and the reasoning is stated at /agents/
- Content last updated: 2026-08-20

## Machine-readable

- [/agents/SKILL.md](/agents/SKILL.md): This contract as agent instructions
- [/llms-full.txt](/llms-full.txt): Complete content index with all page URLs and descriptions
- [/.well-known/security.txt](/.well-known/security.txt): Security contact (RFC 9116)