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

Annotations already declare readOnly, idempotent, and non-destructive behavior, so the burden is lower. The description adds useful behavioral context: it aggregates both fighters, conditionally returns a booked bout 'if one exists', and includes model-generated win probability, which conveys that the result is a computed comparison rather than a static record.

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 a single information-dense sentence with the core verb and resource front-loaded ('Head-to-head in one call'). Every clause corresponds to a distinct output category, and the final 'tale-of-the-tape tool' metaphor is short and memorable without padding.

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 no output schema, the description serves as the return contract, and it is thorough: it covers bios, career statistics, strike/position data, win streaks, previous meetings, common opponents, bout status, model probability, and ratings. Combined with the fully documented parameters, an agent has everything needed to invoke the tool 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 description coverage is 100%, with both a and b documented as fighter slugs or numeric ids and b constrained to differ from a. The description adds no additional parameter semantics, but it does not need to because the schema already carries the full 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 opens with 'Head-to-head in one call', making the comparison function explicit, and enumerates the exact resources returned (bios, stats, meetings, common opponents, bout, probability, ratings). The closing 'tale-of-the-tape tool' reinforces its distinct identity versus single-fighter getters like get_fighter.

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 phrase 'Head-to-head in one call' makes the intended use case clear: use this when both fighters need to be compared in a single request. It does not explicitly name alternatives or state when not to use it, but the context is sufficient to avoid confusion with get_fighter or search_fighters.

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