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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds real behavioral context by detailing the aggregation dimensions (whole event vs per map, round win rates, per-team compositions) that the agent would otherwise have to infer from the output 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?

Purpose is front-loaded in the first sentence and the trailing sentences are short and functional (id source, sibling pointer). The opening sentence is dense with field lists, but every clause maps to actual returned content, so little is wasted.

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 and annotations covering the read-only profile, the description needn't explain return structure or safety. It covers purpose, the single input's provenance, and a sibling alternative, leaving only minor sibling contrast (vlr_event_stats) unstated.

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% and there is only one parameter, so the baseline is met by the schema alone. The description adds value by stating the id is numeric and sourced from vlr_events, which clarifies format and provenance beyond the schema text.

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 (Returns) and resource (agent pick-rate matrix of one VLR.gg Valorant event), and enumerates the exact content: games played, attack/defense round win rates, pick percentages, per-team compositions per map. It also distinguishes itself from vlr_stats, so an agent can tell it apart from siblings without opening a 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?

Explicitly routes the agent to vlr_stats for per-player agent usage and instructs that the id must come from vlr_events, giving a prerequisite and one clear alternative. It does not contrast with the closely related vlr_event_stats, which leaves a small gap, but the when-to-use context is solid.

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