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

Annotations already declare readOnly/idempotent/non-destructive, so the description correctly focuses on value-adds: a concrete credit cost ('Costs 3 credits'), the derivation rule ('all counted from scores'), and a data-availability limit. It does not describe response timing, caching, or what an empty result looks like, which keeps it below 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?

Front-loaded with the use case, followed by the metric list, the exclusion, the parameter caveat, and the cost — each element earns its place. The metric enumeration is dense but appropriate since it defines the tool's scope; the paragraph form is slightly harder to scan than a short structured list.

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 present, the description need not explain return shapes, yet it still scopes the metric set and data provenance. It omits how season interacts with the round/ranking breakdowns (aggregate vs per-season) and leaves the league/tour naming mismatch for the agent to resolve, which are the main residual gaps.

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?

The schema documents all three parameters at 100% coverage, so the baseline is 3. The description adds a genuinely useful operational hint ('on the shared endpoint pass league: "wta"'), but it also introduces confusion by describing the tour values as 'atp (default) or wta' while the schema enum is ['tennis','wta'] with a 'tennis' default — an agent must reconcile 'atp' with 'tennis' itself.

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 and resource ('a player's match statistics by season') and then enumerates exactly which metrics are returned (wins, losses, sets, tiebreaks, deciding sets, 6-0 sets, retirements, plus breakdowns by round and opponent ranking). This is clearly distinguishable from siblings like get_player_matches (raw matches), get_surface_splits (surface dimension), and get_head_to_head (two-player comparison).

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?

'Use for a player's match statistics by season' gives a clear activation context, and 'No serve statistics: they are not available' sets an explicit boundary on what this tool can answer. It stops short of naming alternatives for adjacent questions (e.g., surface splits or head-to-head), so routing is implied rather than spelled out.

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