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

Annotations already signal idempotency and non-destructiveness. The description adds meaningful behavioral context beyond annotations by disclosing that timezone determines how daily totals, streaks, and adherence windows are bucketed (defaulting to UTC), and that weight serves as a fallback bodyweight for bodyweight-inclusive volume. This enriches the agent's understanding of side effects and dependencies.

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?

The description is two concise sentences, front-loaded with the main purpose, followed by two high-value caveats. No filler words; every sentence adds necessary context.

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 17-parameter tool, the description is relatively brief. It covers the key behavioral nuances (timezone bucketing and weight fallback) but does not explain whether unspecified fields are left unchanged or reset, nor any validation constraints. The idempotent annotation helps, but a bit more detail on partial-update behavior would increase completeness.

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 only 35% (6 of 17 parameters). The description meaningfully explains only timezone and weight, leaving the other 11 parameters without semantic elaboration. Given the low coverage, the description should compensate far more to clarify parameter meanings and interactions.

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 description opens with a clear verb and resource: 'Upsert the current app user's fitness profile.' This precisely states the action and distinguishes it from siblings like get_profile (read) and log_* (data logging) tools. The unique scope 'current app user' also disambiguates from any multi-user context.

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 provides clear operational guidance, most notably 'Set timezone first' and explains the consequences of timezone and weight semantics. It implies usage for profile updates but does not explicitly contrast with alternative tools such as get_profile, though the tool's unique resource makes exclusion implicitly obvious.

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