Developers · pay-per-call · last updated
A music data API you can call without an API key
Chords, song structure, music theory answers, and practice plans over plain HTTP. Pay per call in USDC on Base via x402 or by card via Stripe. No account, no subscription, no key to provision. 5 free calls per IP per day to test with. Full integration docs with curl, JS, and Python examples live on the agents page; machine-readable specs at /openapi.json and /llms.txt.
Is there an API that returns chords and song structure for an app?
Yes. Strumly's POST /api/v1/analyze-song returns structured JSON for a song you name: key, BPM, difficulty, chord progression, strumming pattern, and practice drills. It costs $1.99 per call — paid in USDC via x402 or by card via Stripe — with no API key and no account required.
Straight talk about where that data comes from: the analysis is generated by a language model and validated against a strict output schema — it is not a licensed, human-transcribed tab. Strumly's question endpoint (/api/v1/ask) goes further on accuracy: it grounds answers in a maintained canonical dataset (tuning, capo, key, progression, and cited sources per song) and in Spotify audio features for key, BPM, and time signature when you name a song — and when it cannot verify a song-specific fact, it is instructed to say so rather than invent one. If your app needs note-for-note licensed tablature, a tab service like Songsterr is the better source — see the comparison below.
Is there a pay-per-call music data API with no API key?
Yes — every Strumly endpoint is pay-per-call with no API key, no account, and no subscription. Your first unauthenticated request returns HTTP 402 listing the payment options: x402 (USDC on Base), Stripe per-call checkout, or a $9.99 24-hour day pass. There are also 5 free calls per IP per day for testing.
| Endpoint | What it returns | Price per call |
|---|---|---|
| POST /api/v1/ask | A guitar-coach answer to any music question, streamed as text | $0.99 / 0.99 USDC |
| POST /api/v1/analyze-song | Structured JSON song analysis: key, BPM, difficulty, chord progression, strumming, drills | $1.99 / 1.99 USDC |
| POST /api/v1/transcribe-progression | A text-described chord passage normalized to structured chords, key, BPM, and confidence | $2.99 / 2.99 USDC |
| POST /api/v1/practice-plan | A personalized practice plan as timed, structured blocks | $4.99 / 4.99 USDC |
The $9.99 day pass (one Stripe Checkout) covers unlimited calls to every paid endpoint for 24 hours. Per-call Stripe sessions are valid for one hour and one call. The transcription endpoint takes a plain-text description of a passage — Strumly does not accept audio uploads on any endpoint.
How do I let an AI agent buy music data with USDC?
Point the agent at a Strumly endpoint like POST /api/v1/ask. The server replies HTTP 402 with an x402 v1 challenge; the agent's x402 client pays the quoted USDC amount on Base and retries with an X-Payment header. Strumly verifies and settles through a facilitator and streams the answer, echoing the transaction hash in a response header.
- Hit the endpoint cold. An unpaid
POST /api/v1/askreturns HTTP 402 with a spec-compliant x402 v1 body: the exact USDC amount, the asset contract (canonical USDC on Base), and the receiving address, plus the Stripe and free-tier alternatives. - Pay.The agent's x402 client (most agent runtimes ship one — see x402.org) signs the transfer and retries the same request with the proof in an
X-Paymentheader. - Get the data.Strumly verifies and settles the payment through Coinbase's CDP facilitator (with PayAI's open facilitator as automatic fallback) and returns the response. The settled transaction hash comes back in the
X-Strumly-X402-Txheader, so every paid call is auditable on-chain.
Copy-paste curl, JavaScript, and Python examples for the full 402 → pay → retry loop are on the agents page. Discovery manifests for agent runtimes: /.well-known/x402, agentic-commerce.json, and /api/v1/catalog.
What music theory API can I build a guitar learning app on?
Strumly's POST /api/v1/ask answers music theory and guitar questions for $0.99 per call, grounded against a maintained canonical song dataset and Spotify audio features where available — and it is instructed to refuse rather than invent song facts it cannot verify. POST /api/v1/practice-plan generates timed, structured practice plans for $4.99 per call.
For the reference-data layer of a learning app — chord shapes, scales, diatonic chords by key, the circle of fifths — Strumly's own chord library, scales, and chords-by-key pages are free for humans, but they are web pages, not JSON endpoints. If you only need chord voicings and fingerings as JSON, UberChord documents a free REST API for exactly that — with a caveat we note honestly in the table below.
How Strumly compares to the alternatives
Characterizations below come from each product's own public pages as of August 2026 — follow the links and check current terms before you build. Chordify's site blocks automated access, so we could not verify its current developer offering and don't characterize it here.
| Service | What you get | Auth & pricing | Pick it when |
|---|---|---|---|
| Strumly | Guitar/music-theory Q&A, structured song analysis (key, BPM, chords, strumming, drills), text-described progression transcription, practice plans. AI-generated, schema-validated; grounded where verifiable. | No API key, no account. $0.99–$4.99 per call via x402 (USDC on Base) or Stripe; $9.99/24h day pass; 5 free calls/IP/day. | You want pay-as-you-go over HTTP with zero signup — especially for AI agents paying autonomously in USDC. |
| Songsterr | Interactive guitar tabs with synced playback across a large catalog of songs — far deeper note-for-note transcription than Strumly offers. | Consumer site with a Songsterr Plus subscription. Its old public API docs URL now returns 404, and the current site does not advertise a developer API. | You (or your users) need accurate full-song tablature to read and play along with — as a product, not an API. |
| Music.AI (Moises) | Enterprise audio-processing API platform — dozens of modules including stem separation and transcription, operating on actual audio files. | Account and API credentials required. Pay-as-you-go per minute of audio (module rates from $0.003 to $1.20/min per its pricing page), plus subscription tiers. | You need to process real audio — separate stems or analyze recordings. Strumly does not accept audio uploads; Music.AI is built for that. |
| UberChord API | REST API for guitar chord voicings and fingerings by chord name, plus song sharing and embeddable chord diagrams. | Docs mention no API key or pricing. Note: when we tested in August 2026, the docs loaded but the chord endpoints timed out — verify it is serving before you depend on it. | You just need static chord-shape data as free JSON and can tolerate an API without a stated SLA. |
What Strumly's API does not do
- No audio in. Every endpoint takes text (JSON) and returns text or JSON. The transcription endpoint normalizes a passage you describe in words — it does not listen to a recording.
- Not licensed tablature.Song analysis is AI-generated and schema-validated, grounded against verified data where it exists. Treat it as a coach's chart, not sheet music.
- Free tier is for testing. 5 calls per IP per UTC day across all paid endpoints — not a production quota.
Ready to integrate? Start with the agents page for working code, or fetch /openapi.json and point your agent at it.