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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds the behavioral scope constraint 'shared matches A vs B only', which is genuinely useful, but says nothing about auth expectations for the optional key, behavior with unknown handles, or result shape.

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 whole definition fits in roughly two lines, with the WHEN clause and sibling contrast front-loaded. The only waste is the leading 'stats_head_to_head.' which merely repeats the name before the useful content begins.

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 a simple two-handle read tool with 100% schema coverage, full annotations and an output schema, the description supplies what structured fields cannot: when to call it and how it differs from stats_bot. Nothing critical is missing for an agent to select and invoke 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% and each parameter already has a description plus a required/optional distinction. The example shows a valid a/b payload, but the description adds no semantic detail about handle format or what 'key' does beyond the schema's own 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?

The description states the resource (head-to-head stats between two handles) and scopes it to shared matches only, which is a meaningful qualifier. It is distinguishable from stats_bot by explicit contrast, though it never uses a direct verb like 'returns' or 'computes' and opens by restating the tool name.

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 'WHEN: rivalry / trash-talk receipts' clause gives a concrete usage context, and it explicitly routes the one-handle case to the sibling stats_bot. It stops short of stating exclusions (e.g., no cross-arena or historical-only lookups) but the alternative is named.

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