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

No annotations are supplied, so the description carries the full burden. It does disclose a genuine behavioral trait — results are gated by the caller's plan/subscription — and 'List' implies a read-only operation, but it says nothing about result shape, whether entries carry identifiers usable with get_holidays, or ordering.

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?

Two sentences, front-loaded with the action and scope, with the filter detail second. The enum enumeration is long but carries meaning; it does partly restate the schema enum, which keeps this from a 5.

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?

For a one-parameter, read-only discovery tool with no annotations and no output schema, the description covers what the tool does and the filter, but leaves the return contract entirely implicit. An agent cannot tell from the text what a 'calendar' object contains or how to chain into get_holidays.

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 coverage is 0%, so the description must compensate, and it partially does: it identifies the single parameter as an optional family filter and glosses each enum value as a calendar family. It does not explain the effect of omitting the parameter or how the families relate to the sibling tools that consume them.

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 and resource ('List published holiday calendars') and adds a scoping condition ('available to your plan') that no sibling states. It stops short of naming how it differs from adjacent discovery tools such as list_financial_centres or list_exchanges, which enumerate members of the same families.

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?

Usage is implied by 'Optional calendar_type filters by family', which tells the agent the filter is optional and what it narrows. There is no explicit statement of when to call this versus the sibling list_* tools, nor what the default (unfiltered) call returns.

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