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

Annotations cover the safety profile (readOnly, non-destructive, openWorld), but the description adds unique operational context: parallel-safe, upstream cost of 1, the API's handling of zero-diff cloned lists, and the caveat that the two lists are not always one week apart with a warning above a ten-day gap. That is exactly the kind of behavioral detail annotations cannot carry.

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-loaded one-line summary followed by labeled sections (When to use / Prefer over / Do not use when) and a short caveat block. Bullets and headers keep it scannable and every sentence carries routing or behavioral 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?

An output schema exists so return values need no explanation, annotations carry the safety profile, and the description covers routing, direction semantics, date resolution, and the week-gap pitfall. An agent has everything needed to select and call it correctly.

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, but the description adds genuine semantics beyond the schema: 'both' means largest absolute change, 'up' is the default, date pins an older list and the default latest resolves past zero-diff clones, and it cross-references division as the standings-tool spelling of tour. Only 'within' and gapDays/comparisonWindow output fields go unelaborated.

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 specific verb+resource+scope: 'biggest climbers/fallers between the latest ATP/WTA list and its predecessor, plus new entries and drop-outs.' It explicitly names the siblings it is not (standings, call_api, player_profile), so an agent can distinguish it without opening any 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?

Gives explicit 'When to use', 'Prefer over' with the reason each alternative is worse (standings = snapshot with no delta; call_api = raw unnormalized rows), and 'Do not use when' routing to standings and player_profile. Nothing is left to inference.

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