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

Annotations already declare readOnly/idempotent/non-destructive, so the burden is lower; the description still adds real behavioral context by stating that DST is handled and that only IANA zone names are accepted. It doesn't describe output shape or error behavior, but the safety profile is firmly established.

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-loads the purpose, then actions, then limits in a dense sequence with no filler sentences. Slightly run-on, but every clause carries 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 an 8-parameter, no-required-argument utility with no output schema, the description covers actions, key parameter meanings, DST handling and zone-name constraints. Return formats and how multiple zones are returned are left implicit, a minor gap against the otherwise thorough coverage.

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?

With only 50% schema coverage, the description compensates by mapping action values to behavior and clarifying that to_tz may be a list and that add operates on days/hours/minutes. It doesn't fully cover the interaction of time/from_tz defaults, but it adds substantial 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?

Opens with a specific verb+resource ('Time zone and date math') and then enumerates each action (now, convert, diff, add) with its effect, so an agent knows exactly what the tool computes. No sibling overlaps this domain, so no differentiation is needed.

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 clear when-to-use ('scheduling across zones or date arithmetic') and explicit when-not limits ('IANA zone names only... no calendars or holidays'). It does not name an alternative tool, which keeps it short of a 5.

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