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

Annotations already declare read-only and idempotent hints, so the description doesn't need to restate those. It adds valuable behavioral context by disclosing that the tool reports whether the US regular session is open, and that a closed-market response refers to the last trading day's close.

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 succinct, front-loaded with the US Stock Info tag, and every sentence adds value: components, usage guidance, no arguments, and the session-status behavior. No wasted words or redundancy.

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 no-parameter read-only market snapshot, the description fully covers what the tool returns, when to use it, and how to interpret the result (including session status). The presence of an output schema means return-value details are already structured elsewhere, so no additional explanation is needed.

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 tool has zero parameters, and the description explicitly notes "Takes no arguments." The empty schema leaves nothing to explain, so the baseline of 4 for zero-parameter tools is upheld.

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 opens with "Get a snapshot of the overall US market" and enumerates the exact components (indices, VIX, yields, commodities, USD/KRW). It explicitly contrasts with single-company tools, making the tool's purpose and scope unmistakable.

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 clearly states "Use this for questions about the market as a whole rather than a single company" and provides concrete example questions. It does not name specific alternative tools, but the contrast with single-company queries is explicit and sufficient for tool selection.

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