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

Annotations declare safe/read-only/idempotent/closed-world, so the safety profile is covered. The description adds real semantic context beyond that: it clarifies the accepted format family (Gregorian, leap-day aware) and states the boolean return, which matters because no output schema exists.

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, front-loaded with the core action, then usage constraint, then return value. No padding or redundancy.

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 no output schema, the description correctly compensates by stating the boolean return contract. Combined with annotations covering safety and a fully documented single parameter, an agent has everything needed to call it correctly.

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 schema already specifies the YYYY-MM-DD format with an example (2024-02-29). The description's 'including leap days' is minor added value over the schema's example, so the baseline 3 is correct.

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 precise verb+resource ('Check Gregorian YYYY-MM-DD calendar dates') and adds scope qualifiers ('including leap days') that tell the agent exactly what is and isn't validated. The distinction from sibling is-* validators is self-evident from the date-specific scope.

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 date-only form fields, not timestamps or timezone offsets' gives an explicit when-to-use and an explicit when-not-to-use. It stops short of naming an alternative tool for the timestamp case, which keeps it from a full 5.

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