Read the water drunk

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety and repeatability are covered. The description adds genuine behavioral context beyond that by disclosing null semantics for each field when unknown, which tells the agent how to interpret partial results.

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?

A single sentence that front-loads the action and resource, then parenthetically lists the returned values and the null case. Every clause earns its place with no filler or repetition of the title.

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?

With an output schema present, return values need not be explained, yet the description still summarizes them and covers the null case; annotations cover the safety profile and the sole parameter is fully documented. The only missing element is routing guidance against overlapping read tools such as get_range_summary or get_progress.

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% and the date parameter's format, required status, and relative-date handling are fully documented in the schema, so the baseline of 3 applies. The description names the day concept but adds no parameter-level meaning (syntax, format, edge cases) beyond what the schema already supplies.

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?

It uses a specific verb (Read) over a specific resource (water drunk on a day) and even enumerates the three returned fields, so the function is unmistakable. It does not, however, explicitly contrast itself with the write sibling set_water or with range/summary siblings like get_range_summary, so it stops short of full 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?

The purpose implies when to call it (fetching a single day's water), and the date parameter's schema description routes relative-date phrasing to get_today. But the description itself never states when to prefer this over set_water or over aggregate tools, nor any exclusion, so usage remains implied rather than stated.

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