garmin-owl

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get_body_composition

Read-only

Retrieve Garmin weight and body-composition measurements for a date range up to 366 days, defaulting to the last 30 days, so you can track body metrics over time.

Instructions

Get Garmin weight and body-composition measurements over an inclusive range of at most 366 days.

Defaults to the 30 days ending on end_date (today when omitted). Use for weight/body- composition history; use get_daily_summary for a day's activity and heart-rate metrics. Returns {start_date, end_date, count, entries}. Missing measurements are not estimated. Weigh-in timestamps are ISO 8601 with an explicit UTC offset and already local.

Requires saved local Garmin authentication (garmin-owl-auth). Reads Garmin and may update the local cache; never changes your Garmin account. Garmin failures are not retried automatically.

Input Schema

Name	Required	Description	Default
`end_date`	No	Inclusive end date, YYYY-MM-DD; omit or pass null for today in the server's local timezone.
`start_date`	No	Inclusive start date, YYYY-MM-DD; must not follow end_date. Range is at most 366 days. Defaults to 29 days before end_date when omitted.

Output Schema

Name	Required	Description
`count`	Yes	Number of weigh-ins returned.
`entries`	No
`end_date`	Yes
`start_date`	Yes
`availability`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed13 schema fields changedv0.3.1Oct 24, 2026

changedInput schema / properties / end_date / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "pattern": "^\\d{4}-\\d{2}-\\d{2}$",
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

addedInput schema / properties / end_date / description

Added value: +"Inclusive end date, YYYY-MM-DD; omit or pass null for today in the server's local timezone."

changedInput schema / properties / start_date / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "pattern": "^\\d{4}-\\d{2}-\\d{2}$",
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

addedInput schema / properties / start_date / description

Added value: +"Inclusive start date, YYYY-MM-DD; must not follow end_date. Range is at most 366 days. Defaults to 29 days before end_date when omitted."

addedOutput schema / $defs

Added value: +{
+  "AvailabilityNotice": {
+    "properties": {
+      "field": {
+        "title": "Field",
+        "type": "string"
+      },
+      "message": {
+        "title": "Message",
+        "type": "string"
+      },
+      "status": {
+        "title": "Status",
+        "type": "string"
+      }
+    },
+    "required": [
+      "field",
+      "status",
+      "message"
+    ],
+    "title": "AvailabilityNotice",
+    "type": "object"
+  },
+  "BodyCompositionEntry": {
+    "properties": {
+      "bmi": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Bmi"
+      },
+      "body_fat_percent": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Body Fat Percent"
+      },
+      "body_water_percent": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Body Water Percent"
+      },
+      "bone_mass_kg": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Bone Mass Kg"
+      },
+      "muscle_mass_kg": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Muscle Mass Kg"
+      },
+      "timestamp": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "description": "Weigh-in time: ISO 8601 with an explicit UTC offset, e.g. 2026-10-09T23:18:16+02:00. The wall time is already local; never add the offset again. The offset is the one Garmin recorded for the device at that moment, or this computer's time zone when Garmin gives only UTC.",
+        "title": "Timestamp"
+      },
+      "visceral_fat_rating": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Visceral Fat Rating"
+      },
+      "weight_kg": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "default": null,
+        "title": "Weight Kg"
+      }
+    },
+    "title": "BodyCompositionEntry",
+    "type": "object"
+  }
+}

addedOutput schema / properties / availability

Added value: +{
+  "items": {
+    "$ref": "#/$defs/AvailabilityNotice"
+  },
+  "title": "Availability",
+  "type": "array"
+}

addedOutput schema / properties / count

Added value: +{
+  "description": "Number of weigh-ins returned.",
+  "title": "Count",
+  "type": "integer"
+}

addedOutput schema / properties / end_date

Added value: +{
+  "title": "End Date",
+  "type": "string"
+}

addedOutput schema / properties / entries

Added value: +{
+  "items": {
+    "$ref": "#/$defs/BodyCompositionEntry"
+  },
+  "title": "Entries",
+  "type": "array"
+}

removedOutput schema / properties / result

Removed value: -{
-  "items": {
-    "additionalProperties": true,
-    "type": "object"
-  },
-  "title": "Result",
-  "type": "array"
-}

addedOutput schema / properties / start_date

Added value: +{
+  "title": "Start Date",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "result"
-]New value: +[
+  "start_date",
+  "end_date",
+  "count"
+]

changedOutput schema / title

Previous value: -"get_body_compositionOutput"New value: +"BodyCompositionList"

First observedv0.1.0Aug 31, 2026

TDQS

A4.7/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare read-only, non-destructive, open-world, but the description adds materially: saved local Garmin authentication is required, the call may update the local cache, it never mutates the Garmin account, and Garmin failures are not retried automatically. It also discloses that missing measurements are not estimated and that timestamps are ISO 8601 with an explicit UTC offset and already local — behavioral facts the annotations cannot convey.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose and scope, then the sibling routing, then return shape, then behavioral caveats. Every sentence carries distinct information; nothing is repeated across lines.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter read tool with a full schema, annotations, and an output schema, this covers everything an agent needs: what it returns, defaults, auth prerequisite, cache side effect, and failure semantics. No call-critical gap remains.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so both parameters are already fully documented with format, inclusivity, and 366-day constraint. The description restates the default window and the range cap but adds no new syntax or edge-case meaning beyond the schema, which is the baseline-3 case.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Get Garmin weight and body-composition measurements') plus the scope constraint (inclusive range of at most 366 days). It explicitly distinguishes itself from get_daily_summary, so an agent can route without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives the selection rule directly: 'Use for weight/body-composition history; use get_daily_summary for a day's activity and heart-rate metrics.' It also documents the default window (30 days ending on end_date, today when omitted), so the agent knows what happens with zero arguments.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.