Threshold is an open-source Garmin MCP server. Ask Claude, ChatGPT or any AI about your training, sleep and recovery, and get numbers computed in code, not guessed. It runs free on your own Cloudflare account.
Why Threshold
Other Garmin MCP servers hand the model raw JSON and hope. Threshold computes every number and shows the rule behind it.
100 fields per item. The model does arithmetic in its head.
| HRV 7-day | 49 ms | normal 51–63 | slightly low |
|---|---|---|---|
| Resting HR | 47 bpm | baseline 46 | +1 |
| Sleep | 7 h 24 | usual 7.3 h | score 82 |
| Body Battery | 71 | 30-day avg 64 | good |
| Form (TSB) | −12 | CTL 58 · ATL 70 | ok |
| Load ramp | 1.34 | ACWR > 1.3 | caution |
Rule: amber = 1 warning or 2+ cautions.
What it does
daily_briefing
HRV, resting heart rate, sleep, Body Battery, training form and load ramp against your own 60-day baselines, with a green, amber or red call.
Hidden VO2 max
Decoded from the FIT file’s undocumented message 140, where Garmin keeps VO2 max and performance condition but leaves them out of the API.
training_load
CTL, ATL, TSB, acute:chronic ratio, monotony and strain, by week and by sport.
analyze_activity
Splits, HR zones, best efforts, power curve, aerobic decoupling and drift, NP, IF and TSS.
query_archive
SELECT strftime('%Y-%m', date) AS month,
SUM(elevation_gain_m) AS climb_m
FROM activities
GROUP BY month ORDER BY climb_m DESC
LIMIT 3;A private D1 archive of every day and activity. Read-only SQL for any question.
Works everywhere
A real conversation
Two questions after a track session, in Claude. Every number below came from Threshold’s tools, not from the model.
Using Threshold, give me some insights about my most recent run.
✓Used analyze_activityYou started too fast: km 1 was 3:22, and km 4 was the slowest at 3:36, a 14 s spread. You recovered in km 5 for a good finish.
HR rose from 176 in km 1 to 196 in km 5 while the pace dropped: cardiac drift under a hard load.
Fatigue shortened your stride rhythm. The cadence drop matches the pace fade in km 4.
Garmin labels it a VO2 max session. At 25–27 °C, the heat added to the drift.
Yes, compare it with every 5K I’ve done.
✓Used 8 tools · list_activities, personal_records, analyze_activity…PB −33 s. Today is your best 5K, 33 s faster than your previous best.
* That run was 5.17 km.
Hold even splits, and don’t start at 3:22.
Only 6 runs have full FIT data, so splits can’t be compared for older efforts. Only runs of about 5 km are counted; a 5K inside a longer run is not included.
Set up · 5 minutes
You need a free Cloudflare account and a Garmin watch that syncs to Garmin Connect. Pick your app:
Cloudflare dashboard → Workers & Pages → threshold → Settings → Variables and secrets → Add. Choose type Secret, enter GARMIN_API_KEY or ACCESS_KEY and the value, then Deploy. If a key is missing, your server’s page says which one and suggests a strong access key.
Connect anything
Apps with a config file send your access key as a bearer token. Replace <you> with your workers.dev subdomain.
{
"mcpServers": {
"threshold": {
"url": "https://threshold.<you>.workers.dev/mcp",
"headers": { "Authorization": "Bearer <ACCESS_KEY>" }
}
}
}{
"servers": {
"threshold": {
"type": "http",
"url": "https://threshold.<you>.workers.dev/mcp",
"headers": { "Authorization": "Bearer ${input:threshold-key}" }
}
},
"inputs": [{ "id": "threshold-key", "type": "promptString", "description": "Threshold access key", "password": true }]
}[mcp_servers.threshold]
url = "https://threshold.<you>.workers.dev/mcp"
bearer_token_env_var = "THRESHOLD_ACCESS_KEY"{
"mcpServers": {
"threshold": {
"httpUrl": "https://threshold.<you>.workers.dev/mcp",
"headers": { "Authorization": "Bearer <ACCESS_KEY>" }
}
}
}{
"mcpServers": {
"threshold": {
"serverUrl": "https://threshold.<you>.workers.dev/mcp",
"headers": { "Authorization": "Bearer <ACCESS_KEY>" }
}
}
}{
"mcpServers": {
"threshold": {
"command": "npx",
"args": ["-y", "mcp-remote", "https://threshold.<you>.workers.dev/mcp", "--header", "Authorization:${AUTH_HEADER}"],
"env": { "AUTH_HEADER": "Bearer <ACCESS_KEY>" }
}
}
}Anything else: Streamable HTTP with OAuth 2.1 (dynamic client registration, Client ID Metadata Documents, PKCE) or a bearer header.
Under the hood
Tools read a D1 archive and fetch only missing or recent days. Recent days are re-checked, because watches sync late.
Every 10 minutes a cron job refreshes recent days and walks back through your history, inside the Workers limits.
Reads a one-hour activity in about a millisecond, 20× faster than Garmin’s JavaScript SDK.
VO2 max = field 7 × 3.5 / 65536 from message 140. Anything less certain is labelled experimental.
Cost: $0
One person’s data is small. The first backfill of a long history takes hours to days on Free; Workers Paid ($5/month, PLAN=paid) does it 5–20× faster.
Privacy and security
Built for one person on their own Cloudflare account. No hosted service; 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.
The Personal API cannot change your Garmin account, and the SQL tool refuses anything but SELECT.
The consent page asks for your access key, shows where tokens go, and warns about local apps.
GPS coordinates, place names and personal identifiers are removed from responses unless you ask.
An MCP server exposes data and tools to AI assistants through the Model Context Protocol. A Garmin MCP server lets Claude, ChatGPT or another assistant read your Garmin Connect data and answer questions about it. Threshold also analyzes the data in code: readiness, training load, HRV baselines and best efforts.
Deploy Threshold to Cloudflare with 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 works on claude.ai, Claude Desktop and the Claude mobile apps.
Turn on Developer mode in ChatGPT, create a connector with your Threshold /mcp URL, choose OAuth, and enter your access key.
No. Threshold uses a revocable Garmin Personal API key that you create in Garmin Connect. It never asks for your password.
Yes. It is MIT-licensed and runs on Cloudflare’s Workers Free plan.
No. The Garmin Personal API is read-only, and so is Threshold.