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

Annotations already declare readOnlyHint=true, so the safety profile is covered; the description adds genuinely useful behavior by disclosing the computation (EV, break-even probability, edge) and stressing that the probability is user-supplied rather than a model prediction. It does not describe how results are presented, how fractional/American inputs are normalized, or edge cases like p=0/100, leaving some behavioral gaps for a calculator.

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 purpose and formula are front-loaded in the first two sentences, with the probability-is-your-input caveat immediately after. The trailing legal/21+ disclaimers consume roughly half the text but are plausibly required compliance language rather than filler.

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 read-only, four-parameter calculation with full schema coverage and no output schema, the description supplies the formulas needed to anticipate return values (EV, break-even, edge) and clarifies the meaning of the one ambiguous input. Only the output shape and odds-format handling remain unstated.

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 baseline is 3, and the description earns an extra point by tying parameters together in formulas: stake in 'EV = stake * (p*(decimal-1) - (1-p))', p in 'break-even probability = 1/decimal' and 'edge = p - break-even'. That clarifies what each input contributes to the output beyond the schema's per-field 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 a specific computation ('Expected value of a wager from odds and your own win probability') and even spells out the formula, so the resource and operation are unambiguous. It never names a sibling, but the EV/break-even/edge framing clearly separates it from convert_odds and parlay_payout on inspection.

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?

Usage is only implied: an agent can infer you call this when you have odds plus an estimated win probability and want EV. There is no explicit 'use this instead of X' routing to convert_odds or parlay_payout, and no stated prerequisites beyond the 21+ notice.

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