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

With no annotations, the description carries the full burden, but it only states the simple behavior of returning current time. It does not mention error handling for invalid zone names, output format, or that only the 'zone' parameter is used while others are ignored (though the schema descriptions note discarding).

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?

A single, front-loaded sentence with no filler. It is appropriately sized for the tool's simplicity and wastes no words.

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?

The description is complete for a simple timezone lookup, and the schema fully documents parameters, including noting that irrelevant ones are discarded. However, it does not describe the output format or edge cases, and the abundance of unrelated optional parameters could confuse an agent without the schema's discarding notes. Overall adequate but with minor gaps.

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 each of the 9 parameters having a description, including 'zone' as IANA timezone name. The description itself adds no extra meaning beyond what the schema provides. Baseline of 3 is appropriate since schema handles the semantics, though the description does not highlight that only 'zone' matters.

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 'Current time in a named IANA timezone' is a clear verb-resource pair that states exactly what the tool does. It distinguishes from siblings like utc-time (which likely returns UTC) and iana-zones (which lists zones), focusing on a specific named timezone lookup.

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?

No guidance is provided on when to use this tool versus alternatives such as utc-time or iana-zones. There is no mention of when-not, prerequisites, or typical scenarios. An agent must infer usage from the description alone.

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