# THIRI

> THIRI (Tonal Harmony Intelligence Rhythm Interface) is a deterministic harmony engine for music software and AI agents. Given a chord symbol, a key or a progression, it returns the pitch-class analysis, resolutions, voicings and reharmonisations computed from pitch-class-set theory, so the same input always gives the same answer. Built by Blues Prince Media in Montreal.

## What it does

Five tools, available over MCP and REST (https://chords.thiri.ai/v2):

- analyze_chord: name a chord, get its pitch classes, quality, extensions and function in a key.
- resolve_chord: where a chord wants to go next, ranked.
- generate_voicing: close, drop 2, drop 3, drop 2+4 and chord voicings inside a playable range with voice leading.
- reharmonize: substitutions for a progression that keep the melody legal.
- conduct_band: a full ensemble pass over a progression: voicings per instrument, bar by bar.

## Get started

- Free API key (1,000 calls a month): https://build.thiri.ai/keys
- Paid plans on the same page: $5 a month and $20 a month for higher quotas.
- Docs: https://build.thiri.ai/docs
- Manual: https://build.thiri.ai/manual
- API reference on this site: https://thiri.ai/developers.html
- MCP server package: @bluesprincemedia/thiri-mcp on npm (https://www.npmjs.com/package/@bluesprincemedia/thiri-mcp), source at https://github.com/BluesPrince/thiri-mcp

## Licensing

- The MCP server is PolyForm Noncommercial: free for personal, research and noncommercial use.
- Commercial licence to ship the MCP inside a product you sell: $1,200 a year, https://build.thiri.ai/keys?plan=licence
- Licence terms: https://thiri.ai/licensing/mcp/
- Embedded builds for hardware (per unit): https://thiri.ai/licensing/

## Try it

- Browser demos, no account: https://demo.thiri.ai
- Every surface the engine runs on: https://thiri.ai/play.html
- Research notes and measurements: https://thiri.ai/research/

## Products built on the engine

- FYLLM: score your AI video on your Mac, from $47. https://bluesprincemedia.com/fyllm
- Composer C, the agentic Csound DAW: https://composer.thiri.ai
- Run the Changes, the practice tool: https://runthechanges.com

## Community

- T.H.I.R.I. Builders on Skool (community only, no checkout): https://www.skool.com/thiri-builders-6682
- GitHub: https://github.com/BluesPrince

## Contact

dennison@bluesprincemedia.com