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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the bar is lower. The description still adds genuinely useful operational context beyond them: metered/account-scoped access and delay, 'never infer coverage from an empty result,' a single bounded request with no background polling or retry, and the affiliate 27 exclusion. It does not describe pagination or snapshot completeness limits, keeping it out of 5 territory.

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?

Purpose is front-loaded, but the opening is a run-on with a missing sentence break ('...for a sport and date Returns events with...'), and the trailing sentences ('No wagers, account changes or guarantee of returns') read as boilerplate. Several sentences earn their place; a few do not.

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 explained, and the description covers the operational concerns an agent needs (account-scoped access, no retry, empty-result caveat, affiliate exclusion). What is missing is routing versus the closing/event-level siblings, which is the one gap for a tool in this crowded family.

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?

Top-level schema description coverage is reported at 0%, but the nested path/query properties carry extensive documentation (sportID common values, offset in minutes, market_ids limits, affiliate_ids semantics), so the schema is doing the heavy lifting. The description itself contributes only 'use returned canonical IDs,' which is a weak tie-in to the response rather than clarification of the two input parameters. Baseline 3 is appropriate given the schema's visible richness.

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+resource (get opening lines for a sport and date) and adds real substance: 'earliest recorded price for each available line at each sportsbook.' That distinguishes it from the many closing/event-level siblings. It does not explicitly name v2GetClosingBySportAndDate or v2GetEventOpeners, so the agent must infer differentiation from the name and the word 'opening'.

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?

Gives some contextual guidance ('opening snapshots are available whenever a price has been recorded, including before, during, or after an event'), which tells the agent when snapshots exist. However, it never states when to use this over v2GetClosingBySportAndDate, v2GetEventOpeners, or v1GetOpenersBySportAndDate, and offers no exclusion guidance. Usage is implied rather than directed.

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