Your first answer in five minutes

1. Get your key Go to build.thiri.ai/keys, sign in, click Create key and copy it right away. It is shown once. The free tier is 1,000 requests a month, no card.
2. Plug THIRI in Pick your client. Replace YOUR_KEY with the key from step 1.
   Claude Code Claude Desktop curl Node Python

   Claude Code copy

   claude mcp add thiri --env THIRI_API_KEY=YOUR_KEY -- npx -y @bluesprincemedia/thiri-mcp

   Claude Desktop copy

   {
     "mcpServers": {
       "thiri": {
         "command": "npx",
         "args": ["-y", "@bluesprincemedia/thiri-mcp"],
         "env": { "THIRI_API_KEY": "YOUR_KEY" }
       }
     }
   }

   curl copy

   curl -s https://chords.thiri.ai/v2/analyze \
     -H "Authorization: Bearer YOUR_KEY" \
     -H "Content-Type: application/json" \
     -d '{"chord":"Dm7b5","key":"C"}'

   Node copy

   const res = await fetch("https://chords.thiri.ai/v2/analyze", {
     method: "POST",
     headers: {
       Authorization: `Bearer ${process.env.THIRI_API_KEY}`,
       "Content-Type": "application/json",
     },
     body: JSON.stringify({ chord: "Dm7b5", key: "C" }),
   });
   const chord = await res.json();
   console.log(chord.numeral, chord.function); // iiø7 predominant (borrowed)

   Python copy

   import os, requests
   
   r = requests.post(
       "https://chords.thiri.ai/v2/analyze",
       headers={"Authorization": f"Bearer {os.environ['THIRI_API_KEY']}"},
       json={"chord": "Dm7b5", "key": "C"},
   )
   chord = r.json()
   print(chord["numeral"], chord["function"])  # iiø7 predominant (borrowed)

3. Ask for a 2-5-1 In Claude, start the prompt with "Using THIRI," so the model calls the engine instead of answering from memory, and say yes when it asks permission to use the tool.

   prompt copy

   Using THIRI, give me a 2-5-1 in F and explain what each chord is doing.

   You get Gm7, C7 and Fmaj7 with every note spelled, the roman numerals, and each chord's job. Over REST the same question is three /v2/analyze calls, one per chord.
4. Read it like a musician Look at the sevenths. The F in Gm7 slides down a half step to E, the third of C7. The B♭ in C7 slides to A, the third of Fmaj7. That guide-tone line is what makes a 2-5-1 sound like a 2-5-1, and THIRI hands it to you with the theory attached. Try the voice-leading story to see it move.

Three more prompts

Prompt	What comes back
Using THIRI, voice a C13 for jazz piano in the key of F.	A rootless voicing with the 3rd and 7th kept as guide tones and the 13th taking the 5th's seat.
Using THIRI, reharmonize Gm7 C7 Fmaj7 with a tritone sub and explain why it works.	C7 becomes G♭7: same guide tones, bass sliding down a half step into F.
Using THIRI, arrange a 4-bar swung loop in F for piano, bass and drums and give me the MIDI.	A tempo, a groove, a lane per instrument, a lead sheet and a MIDI file you can drop into your DAW.

No install at all

Claude's web and mobile apps can add THIRI as a custom connector. The hosted server is at https://mcp.thiri.ai/mcp and authenticates with your key as a bearer token. Details on the MCP page.

If something breaks

Symptom	Fix
THIRI is not in the tools menu	Quit Claude completely (Cmd+Q on Mac), not just the window, then reopen it.
The config shows an error	The file is picky about commas and braces. If other tools are already there, put the "thiri" block inside the existing "mcpServers", separated by a comma. Do not add a second "mcpServers".
npx not found	Node is not installed or Claude cannot see it. Install the LTS from nodejs.org and restart Claude.
Key rejected, or you lost it	The key goes inside the quotes with no spaces. Lost it? Make a new one at /keys; keys cannot be recovered.
Claude answers without THIRI	Start with "Using THIRI," and say yes when Claude asks permission to use the tool.
HTTP 429	You hit the per-minute limit or the monthly quota. See keys, tiers and limits.