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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so safety is covered. The description adds genuinely useful behavioral context beyond that: the exact set of 13 supported calendars and the operational 1900-2100 year boundary, which is a real constraint an agent must respect.

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 sentences, but the first duplicates the title verbatim and the fragment 'Gregorian date in all calendars' is ambiguous and low-value. The new information (calendar list, 1900-2100 range) is buried at the end rather than front-loaded.

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 carries the burden of explaining what comes back, yet it never describes the return shape – whether all 13 calendars are returned or only the requested ones, or how the holiday results are structured. It is adequate on inputs and scope but incomplete on outputs for a two-optional-parameter conversion tool.

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% – both parameters (date default today, calendars comma list) are fully documented in the schema. The description's enumeration of calendar ids loosely parallels the calendars parameter but adds no syntax, delimiter, or default guidance beyond what the schema already provides, so the baseline 3 applies.

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 specific verb (convert) and resource (calendar date) and enumerates the target calendar systems, which clearly separates it from siblings like convert_time_zone or convert_units. An agent can identify this tool without opening the schema.

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 implies its use cases (date conversion across 13 calendars, plus holiday dates for Islamic/Jewish/Chinese/Persian) and implicitly scopes them to 1900-2100. However, it never states when to prefer it over alternatives such as public_holidays or is_public_holiday, nor any exclusions, so usage is only implied rather than directed.

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