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

Annotations already cover read-only/open-world, and the description adds genuinely new behavioral facts: the exact cost ($0.002 USDC per successful call), the payment rails (x402 on Base, Solana or Arc), and that failed calls are not charged. It also discloses the data source and that freshness is whatever ESPN currently serves. Only the no-event outcome is left unstated.

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?

Two sentences, front-loaded with the resource and scope, then pricing. Every clause carries information an agent needs; nothing is repeated from the annotations.

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?

An output schema exists, so return-shape detail is unnecessary, and the description supplies source, freshness semantics and cost model. What remains missing is edge-case behavior (no event scheduled) and whether the fights cap truncates the card.

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 the single "fights" parameter already documents its 1–30 range and default of 10, so the baseline applies. The description's "fights in card order" describes the output, not the limiting behavior of the parameter, adding no semantics beyond the schema.

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+resource ("ESPN UFC event card: the current or next UFC event with its fights in card order") and names the fields returned. The source ("ESPN's public site JSON") and the "no date filter" note implicitly separate it from historical-fight siblings like dev_ufcstats or dev_sherdog, though no sibling is named outright.

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?

"Returns the card ESPN serves now; no date filter" implies the right context (live/upcoming cards, not historical lookups), but it never states an alternative for historical queries despite UFC-specific siblings existing. Usage is inferable rather than prescribed.

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