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

Beyond the readOnly/idempotent/openWorld annotations, it discloses that pre-start snapshots are provisional, that period markets use event start time as their cutoff, that lookback depth is plan-dependent, that events may return with no prices, that results must not be read as coverage guarantees, and that there is no polling or auto-retry. These are exactly the behavioral traits an agent cannot get from the annotations.

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 core behavior is front-loaded, but the tail contains boilerplate that restates annotations ('Read-only...') or adds little selection value ('No wagers, account changes or guarantee of returns.', 'Affiliate 27 is excluded.'). Several sentences could be trimmed without losing decision-relevant information.

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 nested two-param, plan-gated historical tool with an output schema, the description covers the important unknowns: provisional snapshots, plan-dependent lookback, empty-result interpretation, and an alternative tool. It omits pagination/offset behavior, which matters given the bounded offset range in the schema.

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 two top-level params (path, query) carry no schema descriptions, but the nested query properties are heavily documented, and the description adds its own semantics for `hide_closed` (omitting or false retrieves completed snapshots) and for how the closing cutoff interacts with period markets. It does not add anything for `offset`, `market_ids`, or `affiliate_ids` beyond what the schema already says.

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 and resource — 'Get closing lines for a sport and date' — and expands it with 'latest recorded price for each available line and sportsbook at or before each event's scheduled start time,' which pins down what a closing snapshot actually is. It does not, however, explicitly distinguish itself from the v1 sibling of the same name or from v2GetEventClosing / v2GetOpenersBySportAndDate, leaving that differentiation to inference.

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 routes the agent away from this tool for a related need — 'Use market history for price changes over time' — and gives a concrete include/exclude rule for closed prices. What is missing is guidance on when to prefer this sport+date closing endpoint over the v1 equivalent or over the per-event closing endpoint.

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