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 usefully discloses that the tool is pure CPU with no I/O and is effectively instant, which tells the agent there are no side effects, no auth needs, and no latency concern. It does not cover behavior on malformed input, negative/zero timestamps, or what timezone an ISO 8601 result is rendered in.

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?

One sentence with zero filler: the conversion direction, accepted formats, unit variants, extra output, and performance profile all come through in order of importance. Nothing could be removed without losing information.

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 trivial one-parameter tool, this is close, but with no output schema the description must carry the return-value burden, and it only says 'with relative age'. It does not state whether both an ISO string and a relative-age string are returned, nor the assumed timezone, which are the likely ambiguities an agent would hit.

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?

The schema already documents the single parameter at 100% coverage, so the baseline is 3. The description earns a point because it adds semantics the schema lacks: the accepted unit distinction (seconds versus milliseconds) and the fact that relative age is computed alongside the conversion.

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?

The description gives a specific verb and resource pair ('Convert between Unix timestamps ... and ISO 8601 dates'), plus explicit scope details: seconds versus milliseconds, both directions, and relative age. It does not, however, distinguish the tool from the near-duplicate sibling 'convert_timestamp' (or 'time_convert'), so an agent cannot tell from this text alone which one to pick.

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 phrase 'both directions' implies bidirectional use, but the description never says when to choose this tool over the obvious alternatives in the sibling list, especially 'convert_timestamp', 'time_convert', 'timezone', and 'date_calc'. No exclusions, prerequisites, or selection criteria are given.

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