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

Annotations already establish read-only, idempotent, open-world, non-destructive behavior, and the description adds genuinely useful context on top: snapshots are provisional before event start, period markets use the event start as cutoff, plan entitlement governs historical lookback, an event can come back with no prices, and there is no background polling or automatic retry. The trailing boilerplate about wagers and affiliate 27 is weaker, but the operational disclosures are substantive.

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 opening runs two sentences together without punctuation ('...for an event Returns the latest...'), and the final block ('Read-only Product data... No wagers, account changes or guarantee of returns') is generic boilerplate that does not earn its place. The core content is front-loaded and useful, but the tail dilutes it.

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 present, the description correctly focuses on semantics rather than return shape, and it covers the key edge cases for a closing-price tool: provisional snapshots, empty results without prices, plan-dependent lookback, and period-market cutoffs. The main gap is the absence of guidance distinguishing it from the other closing/opener endpoints.

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?

The nested schema already documents every query parameter in depth (market_ids limits, affiliate sentinels, include flags), so the baseline is a 3. The description only adds a restatement of hide_closed's default behavior ('Omit hide_closed or use false...') and says nothing about include, main_line, market_ids, or affiliate_ids, so it does not meaningfully extend parameter understanding.

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 verb+resource ('Get closing prices for an event') and immediately defines what closing means: the latest recorded price per line and sportsbook at or before scheduled start. It partially differentiates from siblings by naming the market-history endpoints as the alternative for time-series data, though it never contrasts with close cousins like v2GetEventOpeners or v2GetClosingBySportAndDate.

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?

It gives explicit routing guidance — 'For price changes over time, use GET /api/v2/events/{eventID}/markets/history' — plus a clear when-to-set rule for hide_closed. What's missing is differentiation from the other closing/opener tools in the sibling set, so an agent still has to infer which closing endpoint applies to its case.

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