Log weight (replaces day)

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

Building on annotations (destructiveHint=true, readOnlyHint=false, idempotentHint=false), the description discloses what gets destroyed (same-day entry overwritten via dayID 'body-{dayStart.epoch}'), the always-on storage path (Vaultbeat cloud + MCP), conditional Apple Health sync gated by an iOS toggle, end-to-end encryption, and the trend-corruption failure mode. It deepens the annotations rather than repeating or contradicting them.

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

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

Purpose is front-loaded and the layout (params → behavior → warnings) is logical, with nearly every sentence earning its place. The deduction is the closing historical note about the 2026-07-28 docstring revision — self-referential documentation history that an agent does not need and that slightly muddies the date timeline.

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

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

For a write tool with destructive overwrite and external Apple Health side effects, the description covers parameter constraints, defaults, storage destination, sync conditions, the corruption failure mode, and the exact user-facing instruction to give. Since an output schema exists, not explaining return values is acceptable, and nothing an agent needs to invoke or reason about this tool is missing.

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

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

Schema description coverage is 0%, so the description carries the full burden for both parameters. It supplies constraints (weight_kg must be positive and ≤500), format and meaning (date is a LOCAL 'YYYY-MM-DD' day), and the default behavior (today) — all absent from the bare schema.

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

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

The opening sentence 'Log the owner's weight (kg) on their behalf' names a specific verb, resource, unit, and acting party, and the title 'Log weight' reinforces it. The body references get_weight_trend as the read counterpart, so an agent can distinguish this write tool from its sibling log_* tools without opening the schema.

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

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

The description gives explicit usage semantics: same-day upsert-in-place overwrite behavior and a default date of today. It also gives an explicit when-not instruction — do NOT tell the owner to re-enter the weight manually, because double-entry corrupts the trend line — plus the correct alternative (enable the 'Allow AI to update Apple Health' toggle), routing the agent's behavior precisely.

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