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 discloses the key behavioral trait: output is always UTC, and local time is added only when a city argument is present. It does not state the return format (e.g. ISO 8601) or note that the operation is a safe read, leaving modest gaps for a zero-annotation tool.

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 tight sentences with the output behavior front-loaded and the usage hint second. No filler, no restatement of the tool name or schema.

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 and no annotations, the description covers what the tool returns and why it would be called. It omits the returned datetime format and whether the city match is case-sensitive, which an agent invoking it might want to know, but the definition is otherwise sufficient for a single optional-parameter utility.

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%, so the baseline is 3, and the description genuinely adds meaning: it explains that supplying 'city' changes the response to include local time, framing the parameter's effect rather than repeating its type. The schema already enumerates valid city values, so the description does not need to restate 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 (Returns) and resource (current date and time) plus scope (UTC, and local timezone when a city is given). Nothing in the sibling set covers this capability, so an agent can select it unambiguously.

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?

Provides a clear use context ('Use it to know what "today" is for the customer'), which tells the agent when this tool is relevant. It does not name alternatives or state exclusions, but no sibling overlaps this capability, so the omission is minor.

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