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

Annotations already declare readOnlyHint and openWorldHint, so the bar is lower, and the description still contributes useful behaviour: the response exposes tabs with a live_count per sport and a default sport is used when event_type_id is omitted. It does not cover pagination or result-size behaviour, but the presence of an output schema removes the need to explain return values.

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 front-loaded sentences with no filler, leading with what is fetched before the parameter behaviour. The second clause is denser than ideal and packs two separate ideas (tabs enumeration and default-sport fallback) into one sentence, but nothing is wasted.

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?

With an output schema, full parameter coverage, and read-only annotations, the description supplies the remaining operational context an agent needs: this is a live/in-play listing, sport selection is optional, and a default sport is used. Only the choice among sibling live endpoints remains unaddressed.

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 restates the event_type_id default behaviour already documented in the schema and clarifies that tabs come from the response, but adds no format or semantics beyond the structured fields for state, market_type, tab, or exclude_markets.

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: fetch FanDuel Sportsbook events 'in play now' for one sport, returning live markets and odds. That scope is clear and separable from the sibling set. It does not explicitly distinguish itself from near-neighbours like fanduel_sportsbook_live_data, live_scores, or live_count, so it stops short of a 5.

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 implied by 'in play now' and it explains the parameter-driven branch (pass event_type_id to load a sport, otherwise the default sport is returned). However, it names no alternatives and gives no when-not guidance against the many other live/event siblings, leaving the agent to infer the selection rule.

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