"Am I recovered enough for intervals today?" · "Is my HRV trending down?" · "Am I ramping up too fast?" · "Break down this morning's run." · "What are my 5k and 10k bests this year?" · "Which months did I climb the most?"

Threshold is a self-hosted Model Context Protocol (MCP) server that connects Garmin Connect to AI assistants. It runs on your own free Cloudflare account and talks to Garmin's official Personal API with your own key. No password, no scraping, no third-party service in between. It works with Claude (web, desktop, iOS, Android), ChatGPT, Claude Code, Cursor, VS Code, Codex, Gemini CLI, Windsurf and any MCP client.

Why Threshold

Other Garmin MCP servers hand the model raw JSON and hope it does the math. Threshold does the math.

	Typical Garmin MCP	Threshold
Readiness, training load (CTL/ATL/TSB, ACWR), HRV baseline	model guesses from raw JSON	computed in code, rules shown
Aerobic decoupling, cardiac drift, best efforts, power curve	no	from the original FIT file
VO2 max and performance condition hidden from the API	no	decoded from the FIT file
Full-history archive with SQL	no	D1 archive, read-only SQL tool
Works on your phone (Claude / ChatGPT mobile)	rarely	OAuth built in
Hosting	your laptop must stay on	Cloudflare free tier, one click
Context-window friendly	100 fields per item	compact, unit-labelled output
Privacy	GPS and names in every response	GPS and identifiers removed by default

What you can ask

Tool	Answers
daily_briefing	"How am I today?" HRV, resting HR, sleep, Body Battery, form and load ramp against your 60-day baselines, with a green / amber / red call and the rule behind it.
recovery_analysis	HRV on a personal baseline (ln rMSSD, 7-day rolling mean, normal band = baseline ± 0.5 SD), resting-HR drift, sleep versus usual.
training_load	Fitness (CTL), fatigue (ATL), form (TSB), acute:chronic ratio, monotony, strain, weekly load, load by sport.
weekly_report	Week-by-week volume, load, intensity split (80/20?), sleep, HRV, resting HR, and change versus last week.
metric_trend	Any metric over time (HRV, resting HR, sleep, weight, VO2 max, running pace, efficiency...), slope, min/max, and comparison with the previous period.
analyze_activity	One workout from its FIT file: splits, laps, HR zones, best efforts, decoupling and drift, NP/IF/TSS, efficiency factor, hidden VO2 max.
personal_records	Fastest 400 m to marathon, 10–100 km rides, swim bests, power curve 5 s–60 min, longest and hilliest sessions.
list_activities	Activities by date, sport, type or name, one compact line each.
query_archive	Read-only SQL over your whole history, for everything else.
get_health_data, get_day_detail, get_activity, get_profile	Garmin's own records, compacted: sleep stages, HRV readings, heart rate, SpO2, stress, Body Battery, weight, hydration, nutrition, menstrual cycle, fitness age.
sync_now, server_status, garmin_api_get	Pull fresh data now, health checks and archive coverage, and raw access to any Personal API path.

Clients that support MCP prompts also get morning check-in, weekly review, analyze last workout and race readiness.

Quick start (5 minutes)

You need a free Cloudflare account and a Garmin watch that syncs to Garmin Connect.

1. Get your Garmin key. Open Garmin Connect → Personal API, click Create, and copy the key. Garmin shows it only once.

2. Deploy. Click the button, sign in to Cloudflare, and finish the deploy.

3. Add your two keys. In Cloudflare open Workers & Pages → threshold → Settings → Variables and secrets → Add variable. Add each one with type Secret, then click Deploy:

Name	Value
GARMIN_API_KEY	the key from step 1
ACCESS_KEY	a password you make up, 20+ characters. You type it once per app you connect.

4. Open your server. Cloudflare shows its address when the deploy finishes: https://threshold.<you>.workers.dev. The page says Ready and shows your MCP URL. If a key is missing, the page tells you exactly where to add it (and suggests a strong access key).

5. Connect Claude. Settings → Connectors → Add custom connector → paste the MCP URL → enter your access key. Other apps are below.

Your history fills in by itself in the background.

Add or change a key later

Cloudflare dashboard → Workers & Pages → threshold → Settings → Variables and secrets → Add. Choose type Secret, enter the name (GARMIN_API_KEY or ACCESS_KEY) and the value, then Deploy.

Deploy from the command line instead

git clone https://github.com/KareemmSayed/Threshold.git && cd Threshold
npm ci
npx wrangler deploy                      # creates the database and KV store on first deploy
npx wrangler secret put GARMIN_API_KEY   # paste your Garmin key
npx wrangler secret put ACCESS_KEY       # paste your access key

Connect your AI

Your MCP URL is https://threshold.<your-subdomain>.workers.dev/mcp. Apps with a connector screen sign in with OAuth: they open your server's page, you type your access key, done. Apps with a config file send the access key as a bearer token.

Claude (web, desktop, iOS, Android)

Settings → Connectors → Add custom connector → paste the MCP URL → Connect, then enter your access key on the page that opens. Add it once on claude.ai and it is on your phone too.

ChatGPT

Settings → Apps & Connectors → Advanced → turn on Developer mode. Then Create a connector, paste the MCP URL, choose OAuth, and enter your access key when asked.

Claude Code

claude mcp add --transport http threshold https://threshold.<you>.workers.dev/mcp \
  --header "Authorization: Bearer <ACCESS_KEY>"

Cursor (~/.cursor/mcp.json), Windsurf (~/.codeium/windsurf/mcp_config.json)

{
  "mcpServers": {
    "threshold": {
      "url": "https://threshold.<you>.workers.dev/mcp",
      "headers": { "Authorization": "Bearer <ACCESS_KEY>" }
    }
  }
}

Windsurf names the field serverUrl instead of url.

VS Code (.vscode/mcp.json)

{
  "servers": {
    "threshold": {
      "type": "http",
      "url": "https://threshold.<you>.workers.dev/mcp",
      "headers": { "Authorization": "Bearer ${input:threshold-key}" }
    }
  },
  "inputs": [{ "id": "threshold-key", "type": "promptString", "description": "Threshold access key", "password": true }]
}

Codex CLI (~/.codex/config.toml)

[mcp_servers.threshold]
url = "https://threshold.<you>.workers.dev/mcp"
bearer_token_env_var = "THRESHOLD_ACCESS_KEY"

Gemini CLI (~/.gemini/settings.json)

{
  "mcpServers": {
    "threshold": {
      "httpUrl": "https://threshold.<you>.workers.dev/mcp",
      "headers": { "Authorization": "Bearer <ACCESS_KEY>" }
    }
  }
}

Any app that only runs local (stdio) servers, e.g. Claude Desktop's config file

mcp-remote bridges stdio to your server:

{
  "mcpServers": {
    "threshold": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://threshold.<you>.workers.dev/mcp", "--header", "Authorization:${AUTH_HEADER}"],
      "env": { "AUTH_HEADER": "Bearer <ACCESS_KEY>" }
    }
  }
}

Anything else: Threshold speaks the standard Streamable HTTP transport with OAuth 2.1 (dynamic client registration, Client ID Metadata Documents, PKCE) or a bearer header.

How it works

 Claude, ChatGPT, Cursor, ...                 Cloudflare Workers (your account)                     Garmin
┌──────────────────────────┐  OAuth or     ┌─────────────────────────────────────────┐   API key ┌──────────────┐
│ "How am I today?"        │──bearer key──▶│  /mcp   16 tools, 4 prompts             │──────────▶│ Personal API │
└──────────────────────────┘               │   ├─ analysis: load, HRV, readiness...  │  24 h     │  (read-only) │
                                           │   ├─ FIT decoder: hidden VO2 max, PRs   │  token    └──────────────┘
                                           │   └─ D1 archive ◀── cron every 10 min   │◀──────────────┘
                                           └─────────────────────────────────────────┘

• Archive first. Tools read from a D1 (SQLite) archive and fetch only missing or recent days from Garmin, split to Garmin's range limits. Recent days are re-checked because watches sync late.
• Background sync. Every 10 minutes the cron job refreshes recent days, walks back through your history a little at a time, and decodes FIT files, newest first. Each run stays inside the Workers request and CPU limits, and backs off when Garmin rate-limits the key.
• Fast FIT decoder. A small decoder written for Workers reads a one-hour activity in about a millisecond, 20× faster than Garmin's JavaScript SDK, which is what makes FIT analysis possible on the free tier.
• Hidden metrics. Garmin writes VO2 max and performance condition into the FIT file's undocumented message 140 but leaves them out of the API. Threshold decodes them (VO2 max = field 7 × 3.5 / 65536, confirmed by the community) and labels anything less certain as experimental. If Garmin strips that data from API downloads, the tool says so.

Does it fit Cloudflare's free tier?

Yes. One person's data is small.

Free-tier limit	Threshold's use
100,000 requests / day	~150 cron runs plus your chats
10 ms CPU / request	Most tool calls use a few ms; one FIT file per cron run (3–10 ms)
50 external requests / invocation	30 per tool call, 12 per cron run
D1: 5 GB, 5 M reads, 100 k writes / day	Years of history fit in a few MB
KV: 1,000 writes / day	A few per day (Garmin token, OAuth)
5 cron triggers	1

The first backfill of a long history takes a few hours to a few days on Free, and FIT files import one per run. On the Workers Paid plan ($5/month) set PLAN to paid and it does everything 5–20× faster.

Configuration

Name	Kind	Default	Meaning
GARMIN_API_KEY	secret	–	Your Garmin Personal API key.
ACCESS_KEY	secret	–	Unlocks your server (16+ characters).
PLAN	var	free	paid does more work per run.
TIMEZONE	var	Garmin profile, else UTC	IANA zone used for "today".
GARMIN_KEY_EXPIRES	var	–	YYYY-MM-DD; tools warn 14 days before.
BACKFILL_FROM	var	as far as Garmin answers	Oldest date to archive.
SYNC_FIT_FILES	var	true	false skips FIT downloads in the background.
PUBLIC_URL	var	request origin	Pin the OAuth origin when you use a custom domain.

Set any of these in the Cloudflare dashboard: Workers & Pages → threshold → Settings → Variables and secrets → Add (type Secret for the two keys, Text for the rest). They survive redeploys.

Key expiry. Garmin keys last 30 days to a year and Garmin emails you about a week before. Create a new key, run npx wrangler secret put GARMIN_API_KEY, and update GARMIN_KEY_EXPIRES. No redeploy needed.

Privacy and security

• Single user, your account. Garmin's terms make the Personal API key personal. Threshold is built for one person on their own Cloudflare account; there is no hosted service and your data never passes through this project.
• The Garmin key never leaves the Worker. It is exchanged for a 24-hour token, cached in your KV namespace.
• Read-only. The Personal API cannot change your Garmin account, and the SQL tool refuses anything but SELECT.
• Only you can connect apps. The OAuth consent page asks for your access key, shows where tokens will be sent, and warns about local apps. Tokens are bound to your server's /mcp URL.
• Less exposure to cloud models. GPS coordinates, place names and personal identifiers are removed from responses unless you ask for them.

See SECURITY.md to report a vulnerability.

Troubleshooting

• Ask your assistant to run server_status: it checks the keys, the Garmin connection, key expiry, archive coverage and the last background run.
• https://<your-worker>/health returns {"ok": true} when the server is configured.
• npx wrangler tail streams live logs.
• Missing older data? The archive fills in the background; server_status shows how far back it has reached.

Limits worth knowing

• Garmin's Personal API does not expose Training Readiness, Training Status or race predictions. Threshold computes its own readiness and load with transparent rules instead.
• Message-140 fields other than VO2 max are community-decoded and labelled experimental.
• Not medical advice. Consumer wearables estimate; trends matter more than single readings.

Development

npm ci
cp .dev.vars.example .dev.vars   # add your keys
npm run dev                      # local server with a local D1 and KV
npm run check                    # typecheck, tests, and a dry-run build

Tests run inside the Workers runtime against a fake Garmin API: the FIT decoder is checked record for record against Garmin's SDK, and the integration tests drive the full OAuth flow, every tool, and the cron backfill.

src/
  index.ts          Worker entry: HTTP and cron
  auth/             OAuth provider, consent and landing pages
  mcp/              MCP server, tools, prompts
  garmin/           API client (token cache, retries, rate limits), endpoints, compaction
  archive/          D1 schema, archive-first sync, backfill, read-only SQL
  fit/              FIT decoder and activity analysis
  analysis/         training load, recovery, readiness, weekly report, trends

Contributions are welcome. Please open an issue first for larger changes.

FAQ

What is a Garmin MCP server?

An MCP server exposes data and tools to AI assistants through the Model Context Protocol. A Garmin MCP server lets an assistant such as Claude or ChatGPT read your Garmin Connect data (activities, sleep, HRV, heart rate, stress, Body Battery, weight) and answer questions about it. Threshold also analyzes that data in code: readiness, training load, HRV baselines, best efforts and more.

How do I connect my Garmin to Claude?

Deploy Threshold to Cloudflare (one click), then in Claude open Settings → Connectors → Add custom connector, paste your server's /mcp URL and sign in with your access key. It then works on claude.ai, Claude Desktop and the Claude iOS and Android apps. See Connect your AI.

How do I connect my Garmin to ChatGPT?

Turn on Developer mode in ChatGPT (Settings → Apps & Connectors → Advanced), create a connector with your server's /mcp URL, choose OAuth, and enter your access key.

Does it need my Garmin password?

No. It uses a Garmin Personal API key that you create in Garmin Connect and can revoke at any time. Older Garmin MCP servers log in with your password through the unofficial garminconnect library; Threshold does not.

Is it free?

Yes. It is MIT-licensed and fits Cloudflare's Workers Free plan. The optional $5/month Workers Paid plan only makes the first history import faster.

Is my data private?

Yes. You deploy it to your own Cloudflare account; your data never passes through this project. Only someone with your access key can connect an app, and GPS coordinates and personal identifiers are removed from responses by default.

What Garmin data can it read?

Activities and their original FIT files, daily summaries (steps, calories, intensity minutes, floors), sleep and sleep stages, HRV, resting and all-day heart rate, stress, Body Battery, SpO2, respiration, weight and body composition, hydration, nutrition logs, menstrual cycle, fitness age, heart-rate zones and profile settings.

Can it see Training Readiness, Training Status or VO2 max?

Garmin's Personal API does not return Training Readiness or Training Status, so Threshold computes its own readiness and training load with transparent rules. VO2 max comes from the activity list and is also decoded from each activity's FIT file, where Garmin keeps more precise values.

Can it change anything on my Garmin account?

No. The Personal API is read-only, and so is Threshold.

Which Garmin watches work?

Any device that syncs to Garmin Connect: Forerunner, Fenix, Epix, Enduro, Venu, Vivoactive, Instinct, Edge bike computers and more. Some metrics (HRV, Body Battery) need a watch that records them.

Credits

Endpoint paths follow Garmin's own Personal API client. FIT field names and scales come from Garmin's FIT SDK. Hidden-field decoding builds on work shared by the Garmin developer forums, intervals.icu and Runalyze communities.

Threshold is not affiliated with or endorsed by Garmin. Garmin and Garmin Connect are trademarks of Garmin Ltd. or its subsidiaries.

License

MIT