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

Annotations already mark this as read-only, idempotent, and non-destructive. The description adds important behavior beyond that: forecasts are model-based rather than live, and an optional API key can select Pro mode. It could disclose more about update frequency or data sources, but it adds meaningful behavioral context.

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?

Two compact sentences, front-loaded with the core purpose and followed by the authentication note. Every sentence adds value and there is no filler.

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 tool with only two parameters, enumerated values, a read-only/idempotent annotation profile, and an output schema, this description is complete enough for an agent to select and invoke it correctly. It covers the asset scope, the non-live nature of the data, and Pro-mode access behavior.

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 description coverage is 0%, so the description must compensate. It names S&P 500, VIX, and Russell 2000, which maps well to the indicator enum, and mentions the optional API key behavior. However, it does not explicitly explain the timeframe parameter or its default, leaving some burden on the schema's self-describing enums.

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 specifies a clear resource (US equity outlook) and names the exact indicators: S&P 500, VIX, and Russell 2000 volatility. It also distinguishes itself from sibling tools by emphasizing model-based forecasts rather than live prices.

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 clear context for use: US equity forecasting, not live market price queries. It does not explicitly name sibling alternatives or say when not to use it, so it stops short of full routing guidance.

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