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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the x402 pricing model ($0.002 USDC per successful call, specific chains), that failed calls are not charged, and geographic coverage limits (US tracks, CAN for Canada). Cost and billing-failure semantics are exactly the kind of thing an agent needs before invoking a paid tool and are not derivable from annotations.

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 core purpose, then the two output modes, then exclusions, then pricing. Dense semicolon-chained clauses pack a lot in without waste, though the first sentence is long enough that the response-mode distinction could have been broken out for faster scanning.

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?

Covers purpose, both parameter-driven response modes, coverage limits, exclusions, and billing behavior. An output schema exists so return structure need not be restated, and nothing an agent needs to decide whether and how to call it is missing.

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%, so the baseline is 3; the description adds real value by tying the optional race parameter to a distinct response shape and by reinforcing the track-code convention (BEL) and date format in context. It does not add enum constraints or validation rules beyond the schema, keeping it at 4 rather than 5.

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 ('Horse racing entries from Equibase's free entry pages'), plus the scoping axes (track and date) and the two response modes (race card vs. field). No sibling tool covers horse racing, so it is trivially distinguishable, and the contents enumerated (purse, distance, surface, jockey, morning-line odds) make the tool's output identity unambiguous.

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?

Explicit exclusions are given ('No past performances or results'), and the race parameter is framed as optional with the consequence stated ('without it the race card is returned'). It stops short of naming alternatives, but no sibling tool covers this domain, so there is little to route against.

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