fitatu-api

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Log body weight

log_weight

DestructiveIdempotent

Save your body weight in kilograms for a specific date, replacing any existing weight for that day while keeping other measurements.

Instructions

Save the user's body weight for a day in kg, replacing a weight already saved for that day; other body measurements of that day are kept. data.ok says the server accepted it.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`date`	Yes	Day as YYYY-MM-DD; when the user says today, yesterday, this week or a weekday, call get_today and count from its date.
`weight_kg`	Yes	Body weight in kg; convert pounds first (1 lb = 0.4536 kg).

Output Schema

TableJSON Schema

Name	Required	Description
`ok`	Yes
`data`	No
`error`	No	describe_error() of what went wrong; docs/AGENTS.md, Results and errors.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 16, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare destructiveHint, idempotentHint and readOnlyHint=false. The description adds genuinely useful behavioral context beyond them: the write replaces only the existing weight for that day while other body measurements are preserved, and the 'data.ok' acceptance signal clarifies what success looks like.

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?

A single tightly written sentence that front-loads the action and scope and appends the replacement rule and response signal with no wasted words.

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

Completeness4/5

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

For a two-parameter mutation with full schema coverage and an output schema, the description covers mutation scope, preservation of other measurements, and response semantics. The data.ok mention is slightly redundant against the output schema, but nothing an agent needs to call the tool correctly is missing.

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 description coverage is 100%, so both parameters are fully documented in the schema (including the YYYY-MM-DD format, lb conversion, and get_today redirect). The description's 'in kg' and 'for a day' only restate the schema, adding no new semantics.

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

Purpose4/5

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

The description uses a specific verb+resource ('Save the user's body weight for a day in kg') and clarifies the scope is a single day's weight, which distinguishes it from the sibling log_measurements. It stops short of naming that sibling explicitly, so it falls just below the top tier.

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

Usage Guidelines3/5

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

No explicit when-to-use guidance or named alternatives are given. Usage is only implied via the 'for a day' scoping and the replacement behavior, so an agent must infer that this is the tool for logging weight versus broader measurement logging.

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