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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower. The description adds genuinely valuable semantics beyond them: days shift the calendar date and preserve clock time while hours/minutes count real elapsed time, so DST transitions inside the span are handled correctly. It does not cover range limits or error behavior, which keeps it short of 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?

Three sentences, front-loaded with the action and result, then the semantic rule, then the routing alternatives. No filler and nothing repeated from the schema.

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?

Annotations carry the safety profile, an output schema exists so return format need not be described, and all seven parameters are documented in the schema. What remains for the description — the DST/calendar-day semantics and sibling routing — is exactly what it covers.

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 100%, so the baseline is 3 and the schema already defines each parameter. The description nonetheless adds meaning the schema does not: the days-versus-hours semantic distinction and the consequence of the time_zone parameter (real elapsed vs. plain 24-hour days).

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 concrete verb+resource: move a date and clock time forward or back by days, hours and minutes, and return the result. It immediately scopes itself to US time zones, which separates it from any generic date-arithmetic sibling.

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?

Names three alternatives (time_duration_between, add_to_date, convert_time_zone) and the exact condition that selects each. An agent can route without opening any schema.

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