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

Annotations already declare readOnlyHint/openWorldHint, and the description adds real behavior on top: results are official for today only, payoffs are broken out per wager type, and refunded races surface a "Refund" payoff instead of a winner. Auth and pagination behavior are left out, but the exceptional-case handling is valuable.

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 returned payload and followed by the use case and filter options. No filler and no repetition of the tool name.

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 values need not be explained, and the description still covers scope, key fields, the refund edge case, and filtering. The remaining gap is pagination/volume expectations and the explicit handoff to the past-race siblings for non-today dates.

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%, so param meaning is already carried by the schema and the baseline applies. The description restates the track/country/race_type filters without adding anything (no note that race_type takes T/H/Q/L codes, no mention of exclude_country or the page/limit paging params).

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?

Specific verb plus resource ("Get today's official FanDuel Racing results") with the returned fields enumerated, so the agent knows exactly what it retrieves. The "today's" scope implicitly separates it from fanduel_racing_past_races / fanduel_racing_race, but no sibling is named explicitly.

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?

"Use it to check who won; filter by track, country and race type" gives a concrete task and the narrowing dimensions. It stops short of saying when NOT to use it — e.g. that earlier dates belong to fanduel_racing_past_races — so the routing decision is only partly covered.

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