suunto-mcp

An MCP server for authoring and managing structured workouts (SuuntoPlus™ Guides) on Suunto, designed so the transport can be swapped without touching the workout model.

Not affiliated with or endorsed by Suunto Oy.

Why it's built this way

There are three possible ways to get a structured workout onto a Suunto watch, and they differ enough that the transport has to be a replaceable part:

suuntool deliberately isn't one of these paths: it has no guide-creation capability at all. What it does have is a good, read-only MCP server of its own — suuntool mcp — for completed activity and wellness data, comments, reactions, and profile info. This server doesn't wrap or re-expose any of that: run the two side by side as separate MCP configs (claude mcp add suunto-mcp -- ... and claude mcp add suuntool -- suuntool mcp) rather than have this one duplicate a surface suuntool already covers better. The private backend's use of suuntool's session file (below) is credential reuse, not functionality overlap — it's the reason suuntool is a prerequisite for the private backend either way, so adding its own MCP server alongside this one costs nothing extra.

Its exit codes double as this server's own error taxonomy: codes 2–7 (USAGE/NETWORK/AUTH_EXPIRED/SERVER/NOT_FOUND/FORBIDDEN) are numerically identical on both, so a session that has expired in suuntool's own session.json surfaces through the same code as an expired Cloud API token.

Related MCP server: coros-training-mcp

The interesting part

The guide format is a display format, not a training format. It has no step roles, no percentages, no nesting, and a 13-character title budget. So the domain model is what a coach would write, and src/compile lowers it:

• roles (warmup/work/rest/…) → titles, notifications and lap marks

• durations → a per-step trigger plus a matching countdown field

• every duration/distance trigger grants lap-skip by default — a compound {type:"or", triggers:[base, {type:"manualLap"}]} plus createManualLap:true, confirmed live against a real Runna guide after a user reported this compiler's own workouts couldn't be skipped early. Opt a step out with allowSkip: false to lock it instead.

• pace ranges → m/s, with the bounds inverted (4:15–4:25 /km is 3.77–3.92 m/s)

• cadence → Hertz (180 spm is 3.0)

• %HRmax / %FTP → absolutes, resolved from the athlete profile

• nested repeats → flattened, keeping the outer block so the step budget survives

• every string truncated and charset-sanitised for the watch display

Correctness is anchored on Suunto's own published sample guide, which is stored verbatim in test/fixtures/ and used two ways: to prove the format model accepts real Suunto output, and as the compiler's target.

Layout

src/domain/     workout model, guide wire format, validator, limits, activity IDs
src/compile/    the lowering compiler, unit conversions, externalId hashing
src/package/    zip packing (manifest.json + guide.json + icon.png)
src/backends/   the GuideBackend port and its implementations
src/mcp/        MCP server
scripts/        APK acquisition and static analysis for the RE track
docs/           captured API contracts and RE findings

Running it

Tool tiers follow suuntool's: read-only by default, --allow-write to create and update, --allow-destructive on top of that to delete. Gating happens at registration, so a tool you have not permitted is absent from the listing entirely rather than present and always refusing.

claude mcp add --scope user suunto-mcp -e SUUNTO_MCP_BACKEND=private -- node /path/to/suunto-mcp/dist/mcp/main.js --allow-write

preview_workout compiles and validates without uploading, and returns the warnings — start there.

For completed-activity and recovery data, add suuntool's own MCP server as a separate config rather than expecting this one to cover it:

claude mcp add --scope user suuntool -- suuntool mcp

Configuration

Configuration is validated at startup and a bad config is a hard exit — an MCP server that starts and then fails every call is much harder to diagnose.

Development

pnpm install
pnpm test
pnpm typecheck

Reverse-engineering track

scripts/pull-apk.sh        # pull the APK off a connected Android device
scripts/analyze-apk.sh     # stage 1: fast dex string scan
scripts/analyze-apk.sh 2   # stage 2: full jadx decompile, only if needed

apk/ and capture/ are git-ignored and must stay that way — captures contain session keys and account identifiers.