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

With no annotations, the description carries full responsibility and excels: it discloses derivation logic for reverify_by and next_effective_known, conditionality on effective_to, handling of 'status unknown', negative behaviors (never parses notes, does not invent dates), and error semantics (402 gate bug). This goes far beyond a typical description.

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?

The description is information-dense and every clause is useful, but it is written as a single run-on paragraph, making it harder to scan. It front-loads the main action and cost signal, but would benefit from bullet points or clearer sentence breaks.

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 explains key derived fields and error codes, but does not give a high-level statement of the return structure (e.g., a list of calendar entries). It is adequate for an informed agent, but a bit more would make it fully complete.

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 100% and both parameter descriptions already include detailed semantics (options, free error codes). The tool description only restates that country and series are optional and adds no new meaning beyond the schema, so a baseline 3 is appropriate.

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 identifies a specific endpoint ('GET /v1/calendar') and scope (this brand's continent), and differentiates from get_changes by stating 'Past changes stay on get_changes.' It is not a tautology and clearly indicates the tool retrieves a calendar, though it does not explicitly name all sibling tools.

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 provides explicit cost/free guidance ('FREE, unmetered'), optional parameters, and a direct when-not reference to get_changes for past changes. It also warns about 402 being a gate bug. However, it does not fully enumerate use cases against all siblings, so it stops short of a 5.

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