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 description only needs to add extra context. It adds meaningful behavioral details: maximum range of 31 days, defaulting to the last 7 days, and the Settings prerequisite. This goes beyond the annotations without 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?

Three short sentences cover purpose, usage trigger, prerequisite, range, and defaults with no filler. The most important scoping information is front-loaded in the first sentence.

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 two-parameter list tool with an output schema, the description is complete: it states what is returned, when to use it, the prerequisite, the allowed range, and the default behavior. Nothing needed for correct invocation or selection 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 coverage is 100%, so the schema already describes both parameters and their defaults. The description adds value by stating the maximum range (31 days) and the default window (last 7 days), which helps an agent validate input without opening the 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 description uses a specific verb ('Review') with a clear resource ('hydration events and stored effective hydration totals'), and the hydration domain distinguishes it from the many list_* siblings. It states exactly what the tool returns without relying on the title.

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 explicitly says 'Use when the user explicitly asks about hydration history or fluid intake' and adds a prerequisite ('Hydration tracking must already be enabled in Settings'). It does not name an alternative tool, but no direct hydration-list sibling exists, so the guidance is clear enough.

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