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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description adds genuinely new behavioral context: a per-call cost of 0.005 USDC via x402 across five named chains, which is not derivable from annotations or schema and materially affects invocation decisions.

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 the use condition, then return shape, then default, then cost, in a tight block of sentences. Slightly dense, but every sentence carries information an agent needs and none 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?

Covers the trigger, return shape, default, and the non-obvious payment cost, and an output schema exists so return values need no further explanation. An agent has enough to call it correctly, though alternative-tool routing is absent.

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%, so both 'at' and 'tz' are already fully documented with accepted formats (ISO 8601, epoch seconds/milliseconds, IANA zones) and defaults. The description repeats the UTC default but adds no syntax or format detail beyond the schema, so the baseline of 3 is appropriate.

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 ('exact time conversion with the right daylight-saving rules') and specifies the return ('ISO time or epoch in any IANA time zone: local time with offset, weekday, abbreviation, DST flag and epoch'). An agent can distinguish this from sibling conversion tools like get_convert or get_fx_rates without opening a schema.

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?

Explicitly frames the trigger with 'Use when an agent needs an exact time conversion with the right daylight-saving rules', which is clear context. However it names no alternatives or exclusions, so the agent gets a clear when but no when-not or sibling routing.

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