Cronometer

Cronometer MCP

An MCP server for your Cronometer account. Ask Claude (or any MCP client) what you ate, what is left for today, how your micronutrients look over the week — and have it log, edit or delete diary entries, with your approval each time.

• The whole diary, with ids. Foods, exercise, notes and biometrics, each with the id the edit and delete tools need, plus the day's targets, what remains, and energy burned.
• Honest nutrition. Totals are computed food by food. A nutrient a food doesn't report is counted as missing, not as zero — so "61 mg of magnesium" comes back as "at least 61 mg; only 4 of 12 foods report magnesium", which is what Cronometer's own total hides.
• Safe writes. Every account-changing tool asks for approval, deletes need an explicit confirmation, a timed-out write is never retried, and a read-only mode removes writes entirely.
• One command to set up, with your password kept in the operating system's credential store. Also runs as a Claude Desktop extension, or as a secure remote connector for claude.ai and the Claude phone apps.

[!IMPORTANT] Cronometer has no public API. This uses the same private interfaces as Cronometer's own app and website, signed in as you. It is unofficial: it can break whenever Cronometer changes them, and Cronometer could restrict an account it sees automated. It is not affiliated with or endorsed by Cronometer. See Risks.

Quick start

Requires Node.js 20 or later.

npx @ekelly95/cronometer-mcp setup

Setup explains the risk and asks you to type ENABLE, then asks for your Cronometer email, password, an authenticator key if the account uses two-factor sign-in, and your diary timezone. It checks the sign-in before saving anything, stores the password in the Keychain (macOS), the Secret Service keyring (Linux) or DPAPI (Windows), and offers to add the server to Claude Code, Claude Desktop and Codex.

Restart your client and ask:

• What did I eat yesterday, and how close was I to my targets?
• How much protein do I have left today?
• Log two large eggs for breakfast.
• Which micronutrients were low this week — and which of those can't be trusted because foods didn't report them?
• Show my nutrient radar for the last 7 days. (renders a chart; see /nutrient_radar)

npx @ekelly95/cronometer-mcp doctor checks the setup at any time.

Other ways to run it

Claude Desktop extension. Download cronometer-mcp.mcpb from the latest release and open it. Claude Desktop asks for your email and password and keeps them in your OS credential store.

Credentials in the client config (for clients without a keyring, or containers):

{
  "mcpServers": {
    "cronometer": {
      "command": "npx",
      "args": ["-y", "@ekelly95/cronometer-mcp"],
      "env": {
        "CRONOMETER_USERNAME": "you@example.com",
        "CRONOMETER_PASSWORD": "…",
        "CRONOMETER_LIVE_ENABLED": "1",
        "CRONOMETER_TIMEZONE": "America/New_York"
      }
    }
  }
}

claude.ai and the phone apps. cronometer-mcp remote-setup configures a Streamable HTTP endpoint with its own single-user OAuth sign-in, run as a user service and published through a tunnel such as Tailscale Funnel. See docs/REMOTE.md.

Tools

46 tools: 24 that read and 22 that write. Dates accept YYYY-MM-DD, today, yesterday or N days ago, resolved in the diary timezone.

Diary and nutrition

Foods, targets, body

Long ranges and downloaded exports

Writes — each asks for approval; ⚠ marks those that also need confirm: true

A write that hasn't yet been verified against a live account says so in its description, and the model is told to read the result back. docs/PROTOCOL.md lists what each tool calls and what has been verified.

Missing is not zero

Cronometer stores each food's nutrients from whatever its source reports. A branded product's label might list eight nutrients; a lab-analysed whole food, ninety. When Cronometer totals a day, a nutrient a food doesn't report is added as zero, so the total looks complete when it isn't.

get_daily_summary keeps them apart. For a made-up day of 12 foods:

A nutrient becomes a number only when every food reports it (or the share you choose with coverage_threshold); otherwise you get a floor that says what it is. Days with nothing logged are listed rather than averaged in as zero. The same rule drives the radar, which draws an incomplete spoke as a dashed "at least" line and a nutrient nobody reported as no data at all. None of this diagnoses anything; it reports what was logged.

How it keeps the account safe

• Approval on every write. Write tools carry MCP's destructive/read-only hints and anthropic/requiresUserInteraction, which makes Claude Code ask every time, under every permission mode. Deletes and other irreversible tools also require confirm: true.
• No duplicate writes. A write that times out is reported as "outcome unknown — check the Cronometer app", never retried. A write is re-sent only when Cronometer refused it outright (401/403), which means it wasn't applied.
• Ids, not guesses. Edits and deletes take ids from get_diary; the server refuses an id that isn't on that day.
• Untrusted data stays data. Food names and notes come back inside a JSON-encoded fence the content cannot close, and the server tells the model to treat them as data.
• Narrow network and storage. HTTPS to cronometer.com and mobile.cronometer.com only, size-capped and time-limited. Passwords live in the OS credential store; session caches are private files (mode 600) in a private directory; secrets are redacted from every error and log line.
• Gentle on Cronometer. Calls run one at a time with a floor between them, and sessions are cached so the server rarely signs in.

Troubleshooting

Risks

• Unofficial interfaces. Cronometer publishes no API. Its terms limit use to personal, non-commercial purposes and allow access to be ended without notice. This tool is for use with your own account only.
• It can break. The mobile API expects the app's version numbers, which can be updated with CRONOMETER_APP_VERSION/CRONOMETER_APP_BUILD; the web protocol's build hashes are discovered automatically. Either can still change in ways only a new release fixes.
• Exports are rate-limited by Cronometer; the export_* tools are for long ranges, and get_diary covers anything up to 14 days without them.
• Not medical advice. Reference intakes are population figures, not personal targets.

How it works

The server talks to Cronometer's mobile API (the Android app's JSON interface) for almost everything, and to the web app's GWT-RPC protocol only for CSV exports, macro templates, fast edits and repeated foods. docs/PROTOCOL.md has the details; docs/DATA_MODEL.md describes the CSV export schemas.

It builds on two MIT-licensed projects: cronometer-api-mcp by Randy Westergren, which established the mobile API, and cronometer-mcp by Paul Hoskins, which established the web protocol. See THIRD_PARTY_NOTICES.md.

Development

npm ci
npm run verify      # typecheck + the full offline test suite
npm start           # run the stdio server from source (after npm run build)

Tests are offline and use synthetic fixtures; nothing in the suite has Cronometer credentials. Live behaviour is checked by hand before a release on a throwaway diary date (docs/RELEASING.md). Changes are recorded in CHANGELOG.md.

License

MIT