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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the write/open-world nature is covered. The description adds real value by disclosing defaults (unitKey='kg', when=now), but says nothing about auth needs, whether it overwrites an existing entry for the same timestamp, or what happens on failure.

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?

Three short, front-loaded sentences with the unit default stated first. The final sentence largely restates the previous two ('when defaults to now' / 'when=new Date()'), which is mild redundancy rather than bloat.

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 simple three-parameter logging tool with no output schema, the description covers the defaults but omits the remaining things an agent needs: the unit context of weightValue, whether a same-timestamp entry is replaced, and the shape of the success response.

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 coverage is only 33%: `when` is documented in the schema and both `unitKey` and `when` defaults are stated in the description, so the description does compensate for the missing enum/date-format detail. However, the required `weightValue` receives no explanation of range, precision, or which unit it is interpreted in, leaving a gap on the one mandatory field.

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?

States a specific verb+resource ('Records a weigh-in'), which an agent can distinguish from get_weigh_ins and delete_weigh_in. It does not, however, differentiate itself from the close sibling add_weigh_in_with_timestamps, so the name/description pair leaves one ambiguity unresolved.

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?

No when-to-use guidance is given and no alternatives are named, despite the sibling add_weigh_in_with_timestamps existing right next to it. The only usable signal is the implicit 'if you want to log a weigh-in, call this', with no conditions or exclusions.

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