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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds real value beyond that by disclosing the exact set of conversions returned (ISO, UTC, epoch seconds/ms, relative time, localized time) and that both second and millisecond inputs are accepted. It does not say what happens on invalid input, so not a 5.

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?

A single front-loaded sentence with no filler; every clause (input formats, output formats, time zone) carries information an agent needs.

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, the description correctly enumerates the returned representations, and the 2-parameter surface is fully covered between description and schema. Only error/invalid-input behavior is unaddressed, a minor gap for a pure conversion 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 50%: timeZone is documented in the schema, but 'value' has no description there. The description compensates by defining exactly what 'value' accepts (Unix seconds or milliseconds, or an ISO 8601 date) and by explaining that timeZone drives the localized output. This adds meaning beyond the schema.

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?

Specific verb (Convert) plus resource (Unix timestamp / ISO 8601 date), and it enumerates the exact output formats produced. An agent can distinguish this from the unrelated siblings (regex, cron, QR, JSON tools) instantly.

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 implicitly scopes usage by naming the accepted input formats (Unix seconds/milliseconds, ISO 8601), which tells the agent when this tool applies. However there is no explicit when-to-use/when-not guidance or named alternative, since the siblings are unrelated utilities. Minimum viable.

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