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

Annotations already declare readOnlyHint=false and idempotentHint=false, indicating a non-idempotent mutation. The description adds the behavioral detail that the action is 'Add', implying it increments existing hydration totals rather than replacing them. This is a useful addition beyond annotations, but it stops short of describing side effects, limits, or response behavior. With annotations covering the mutation profile, a 3 is appropriate.

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 a single, short sentence with no filler. It is front-loaded with the essential action and unit. While it could be more informative, it is appropriately concise for a simple logging tool and avoids verbosity. It earns a 4 for efficiency, though it sacrifices depth.

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?

The tool has six parameters, but only one is required, and the schema explains all of them. The description itself provides no context about optional parameters like destination_id (needed when multiple destinations are writable) or user_query_context (audit forwarding). However, given the high schema coverage and the simplicity of the core action, the description is minimally sufficient. An agent could call it correctly with just the required parameter, so a 3 reflects the adequacy without extra context.

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 100%, so every parameter (milliliters, account, meal_date, destination_id, destination_kind, user_query_context) already has a description. The tool description adds only 'in millilitres', which is redundant with the schema's parameter description. It does not clarify cross-parameter dependencies or provide examples. Baseline 3 is correct given full schema coverage.

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 states a clear verb ('Add') and a specific resource ('hydration in millilitres'), which is unambiguous. However, it does not explicitly differentiate from sibling tools like log_nutrition or log_body_mass, though the specificity to water makes it distinct. It earns a 4 for clarity but lacks explicit sibling differentiation.

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?

There is no guidance on when to use this tool versus alternatives. No mention of when to prefer log_water over log_nutrition, or any conditions like multiple destinations. The description only says what it does, not when to choose it. This leaves the agent to infer usage from the tool name alone.

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