datetime_days_in_month

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

No annotations are provided, so the description carries the full burden. The phrase 'Return the number of days' implies a pure, side-effect-free read, which is the key behavioral trait for a computation tool. However, it says nothing about handling of out-of-range inputs (e.g., month 13, month 0, negative years) or whether an error is raised.

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, front-loaded sentence with no filler. Every word contributes to the purpose, and there is nothing to trim.

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 is trivial and has an output schema, so the return value needs no explanation. Still, for a function accepting arbitrary integers, the description omits any note about invalid input behavior, which is the one piece of context an agent would benefit from here.

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 0%, so the description must compensate. It does name both parameters implicitly ('month and year') and their meaning is clear, but it adds no range or format constraints (e.g., month expected 1-12), leaving ambiguity the schema itself does not resolve.

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 specific verb ('Return') and resource ('number of days in the given month and year'), which is precise enough that an agent knows exactly what the tool computes. It does not, however, explicitly differentiate itself from adjacent datetime siblings such as datetime_is_leap_year or datetime_day_of_week, which also operate on month/year inputs.

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, nor any mention of prerequisites or typical scenarios (e.g., working with calendar calculations or validating dates). The agent must infer usage purely from the one-line purpose.

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