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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds the 'data only' disclaimer and the 'timeline + summary' output shape, which is useful but does not add deep behavioral detail. No contradiction with annotations exists.

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 description is a single sentence that front-loads the core purpose and then adds a concise disclaimer. Every part earns its place, and the format is easy to scan.

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?

The tool is simple: one required parameter, no output schema, and strong annotation coverage. The description communicates the essential return concept—timeline plus summary—for a single replay date. It could mention which sibling supplies valid dates, but the schema already handles that, so the description is nearly complete for this complexity level.

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% because the only parameter, date, is fully described with a format pattern and guidance to use list_history_dates. The description adds minimal parameter-specific meaning beyond confirming it is a single replay date. The baseline of 3 applies when the schema already documents the parameters well.

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 deliverable: a per-day SPX market-structure timeline plus summary for one replay date. It clearly identifies the resource (SPX market structure), the scope (per-day, one replay date), and sets it apart from sibling tools like list_history_dates or get_regime.

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?

The description gives no explicit guidance on when to choose this tool over siblings. It notes that it is data-only and not advice, but does not say when to use get_day versus get_market_structure, get_regime, or other related tools. The parameter schema mentions using list_history_dates for valid dates, but this is not surfaced in the description itself.

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