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

With no annotations, the description carries the full burden of behavioral disclosure, but it only states 'Current UTC timestamp.' It does not specify the output format, whether the value comes from the system clock, or that the four input parameters appear irrelevant to obtaining the timestamp.

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 very short and front-loads the core idea with no wasted words. It is efficient, though it is a noun phrase rather than a complete action sentence and omits important clarifications.

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?

Despite the simple purpose, the description is incomplete for a tool with four optional parameters and no output schema. It fails to state the timestamp format, whether parameters are ignored, or how this tool relates to siblings like 'timezone' and 'ulid-now'.

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?

Although the schema documents each parameter, the parameters (URL, host, JSON, zone) have no evident connection to 'Current UTC timestamp.' The description does not clarify whether these parameters are ignored, optional, or somehow influence the result, leaving the agent confused about how to call the tool.

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 UTC timestamp' clearly identifies what the tool does: it returns the current time in UTC. It is distinguishable from most siblings by its explicit focus on UTC, though it does not explicitly contrast with the similar 'timezone' tool.

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 it should be used when the agent needs the current UTC time, which provides a clear context. However, it gives no explicit guidance about when not to use it or how it differs from 'timezone', 'ulid-now', or other time-related tools.

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