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

The annotations already establish this is a safe, read-only, idempotent call. The description adds genuinely non-obvious behavior beyond those annotations: walkovers are listed but not counted as wins, incomplete records are excluded, and the call costs 3 credits. These are operational details an agent could not infer from structured fields.

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?

The description is front-loaded with the use case and packs useful quirks into a compact block. However, the long enumeration of return fields duplicates the output schema, and the tour/league sentence is denser and more confusing than necessary.

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?

With an output schema and rich annotations already present, the description mainly needs to cover counting quirks and endpoint routing, which it does. It still leaves some ambiguity around how the 'tour' wording maps to the schema's league parameter and does not mention that player IDs can come from search_players.

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 description coverage is 100%, so the baseline is 3. The description does add a useful note to pass league: "wta" for WTA on the shared endpoint, but it frames the choice as 'Tour: atp (default) or wta' while the schema's league parameter defaults to 'tennis' and uses a different enum, creating terminology drift rather than clear added meaning.

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 names a specific two-player resource and enumerates the distinct contents of the report: wins each, sets won, surface and finals splits, and every meeting with score. This clearly separates it from siblings such as get_player_stats or get_match, so an agent can identify the head-to-head tool immediately.

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 opening phrase 'Use for two players' head to head' gives a clear selection condition, and the note about passing league: "wta" on the shared endpoint helps with endpoint choice. However, it does not name alternatives or state when not to use this tool, so it falls short of explicit routing guidance.

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