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

With no annotations, the description carries the full burden and does meaningfully: 'FREE, no key' discloses the auth/no-cost profile and 'IANA zones; handles DST' discloses the accepted input format and a real behavioral edge case. It does not cover return shapes or error behavior, but it adds genuine context beyond the schema.

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 pipe-delimited block, front-loaded with the free/no-key fact and then each action in order. Every clause carries information and there is no filler.

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-output-schema, no-annotation tool, the description covers all four modes and the key input conventions. The main gaps are the default from_tz value and what each action returns, which an agent would have to infer.

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%, and the description compensates by tying parameters to actions ('time from_tz -> to_tz', 'time + days/hours/minutes'), which is the only explanation the undocumented days/hours/minutes parameters receive. It stops short of explaining defaults and the 'list ok' syntax fully, keeping it out of the top band.

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 the resource ('Time zones and dates') and then enumerates every verb via the four actions with their operands (now, convert, diff, add). An agent can tell exactly what the tool does and which action to reach for without opening the schema.

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 action breakdown tells the agent how to select among the tool's own modes, but there is no guidance on when to use this tool versus alternatives such as market_hours or forex_market_hours, nor any exclusions. Usage is implied rather than stated.

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