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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds non-obvious behavioral context beyond that: the pricing for the enumerated choices lives in a separate call (fanduel_sportsbook_builder_quotes), so the agent knows not to expect final prices here, and it discloses the shape of the payload (groups, cards, players, teams). No contradiction with the read-only annotation.

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 is front-loaded in the first clause, followed by payload description and the tool-chain dependencies; nothing is filler. The middle clause ("its groups and cards (bet templates with selectable players, lines and periods), the players and teams offered and every priceable choice") is dense and slightly run-on, which costs a point on crispness.

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 spelled out, and annotations cover the read-only/open-world profile. The description still supplies what structured fields cannot: the data flow from builder_events into this tool and out to builder_quotes, which is what an agent needs to sequence calls. Only minor gaps (e.g., whether results vary by state/market) remain.

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 schema already documents state, event_id and the experience enum values, so the baseline is 3. The description adds real provenance semantics — event_id must be sourced from fanduel_sportsbook_builder_events — which tells the agent where to get a valid value rather than just what type to pass.

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 and resource — get a FanDuel bet-builder experience for one event — and enumerates its contents (groups, cards, players, teams, priceable choices). It also names the two sibling tools in the same family (fanduel_sportsbook_builder_events for input, fanduel_sportsbook_builder_quotes for pricing), so an agent can place it in the family without opening any schema.

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 see what same-game bets can be built" gives explicit intent, and the description states the prerequisite (event_id must come from fanduel_sportsbook_builder_events) and the follow-on step (choices are priced via fanduel_sportsbook_builder_quotes). It lacks an explicit when-not / don't-use-for statement against other odds tools like fanduel_sportsbook_odds or fanduel_sportsbook_market_prices, which is the only missing piece.

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