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

Annotations only say readOnly and openWorld; the description adds genuinely new context — the clock is server-side and reliable, DST is handled, an unknown time zone is not charged, and the call is paid via x402 with a pointer to list_prices. That cost and error behavior is exactly what annotations don't cover. It stops short of describing the failure response for a bad tz beyond the billing note.

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?

Front-loaded with what you get, then the rationale, then the payment caveat — a sensible order for three sentences. Slightly dense with parenthetical asides, but nothing is filler.

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 one optional parameter and no output schema, the description usefully enumerates the return fields (UTC ISO, Unix s/ms, optional local components) so the agent knows what to expect. The only remaining gap is whether a bad tz yields an error body, which is partially signaled by the 'not charged' note.

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 already gives the IANA example, so the baseline would be 3. The description adds real meaning: any IANA zone is accepted, daylight saving is applied automatically, and an unrecognized zone has a stated billing consequence — behavior the schema's 'string, maxLength 2048' does not convey.

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 and resource ('Current time from a reliable server clock') and enumerates exactly what is returned: UTC ISO timestamp, Unix seconds and milliseconds, plus optional local date/time/weekday/offset. No sibling tool overlaps with this, so differentiation is implicit but unambiguous.

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?

'Useful because language models don't know the current date or time' gives a clear condition for when to call it. There are no exclusions or named alternatives, but with no comparable sibling in the list there is nothing to route away from.

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