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

With no annotations, the description carries the full burden. It usefully discloses bidirectionality and a per-call cost ($0.003), which is rare and valuable. It does not, however, state the timezone/UTC assumption in play, what happens if both or neither parameter is supplied, or how invalid input is handled.

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 short sentences plus a cost note, with the core purpose front-loaded and nothing wasted. 'In either direction' is mildly redundant with 'between', a minor trim opportunity rather than a flaw.

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?

For a two-parameter, single-purpose conversion with no output schema and full schema coverage, the description is nearly sufficient; the output form (the other representation) is inferable. The one real gap an agent would care about — assumed timezone for untimestamped dates — is unaddressed.

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 parameters (date as ISO-8601, timestamp in seconds) are already documented. The description only implies 'pass one of the two' and adds no format or precision detail beyond the schema, so the baseline 3 applies.

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 both resources ('Convert between a date and a Unix timestamp') and adds the directionality constraint 'in either direction'. This distinguishes it from siblings like describe_instant or weekday_of, which also take instants but give derived facts rather than raw conversion.

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?

Gives a clear triggering context: 'Use it when a payload carries one and the other is needed.' That tells the agent when the tool is selected, but it names no alternative and gives no exclusions (e.g., when describe_instant would be better).

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