Itu Zones Valid On

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

Annotations already cover the safe-read profile (readOnly, idempotent, non-destructive, closed-world), yet the description adds a genuinely useful behavioral fact: because the source chapter defines no validity window, any listed zone is valid, so the answer will essentially always be affirmative. That pre-empts an agent over-interpreting a 'true' result.

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 short sentences with the core question front-loaded. The 'chapter' framing is slightly lore-dependent but still earns its place by explaining why every zone is valid.

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?

A low-complexity boolean query with a full output schema, so return values need no explanation; the description supplies the one non-obvious fact (validity is effectively universal for listed zones). Only missing piece is a pointer to sibling tools for lookup/search.

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%, with both code (ITU zone number 1-90) and on_date (YYYY-MM-DD) fully documented in the schema. The description adds no further parameter semantics beyond what the schema supplies, 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 question the tool answers (whether an ITU zone was valid on a date) plus the required inputs implicitly. It does not name or contrast against siblings like itu_zones_lookup or itu_zones_search, so differentiation is left to inference.

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 — call it when you need a validity verdict for a zone code on a date — but there is no explicit when-to-use/when-not or named alternative such as itu_zones_lookup. The closing clause about consistent answers across servers hints at context without giving routing guidance.

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