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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds the return shape (L/day plus an electrolyte recommendation), which is helpful context, but with an output schema present and no note on assumptions, defaults, or edge cases, this is mid-range.

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?

Four compact sentences, front-loaded with the purpose and ending with a cross-reference. No filler, though the 'Inputs:' sentence spends words restating parameters incorrectly, which costs a point.

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 read-only calendar-style calculator with full schema coverage and an output schema, the description is adequate, but two gaps matter: the parameter prose conflicts with the actual schema, and there is no differentiation from the water-intake sibling. An agent has enough to call it, but not enough to call it correctly on the first try.

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?

The description actively misdescribes the schema: it lists 'activity hours' where the schema has activity_minutes (default 0, in minutes), and 'temperature °C' where the schema has a climate enum (temperate/hot/cold) with no temperature field at all. An agent following the prose would attempt to pass a numeric temperature and convert hours. This is worse than adding nothing.

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 and resource ('Compute recommended daily fluid intake') and scopes it by weight, activity, and weather, which is clear. However, it never distinguishes itself from the near-identical sibling calculate_water_intake (nor calculate_bread_hydration), so an agent cannot tell which hydration/water tool to pick.

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?

'Use for athletes and outdoor workers' gives a target audience but no when-not conditions and no named alternatives, despite calculate_water_intake occupying almost the same space. The pointer to list_bundles is a navigation aid, not usage guidance.

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