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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and external-data profile is covered. The description adds the key-discovery prerequisite, which is useful, but does not describe what 'details' includes, rate limits, or auth requirements. With annotations covering the safety profile, a 3 is appropriate.

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 short sentences with zero waste. The core action and the prerequisite dependency are both front-loaded and easy to parse.

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?

Output schema exists, so return values need not be explained, and the single parameter is fully covered by schema. The description covers the what and the key-discovery workflow; a minor gap is that it does not mention the sibling yahoo_finance_industry or clarify sector-vs-industry scope.

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%, so the schema already documents the single 'key' parameter as a 'Sector or industry key.' The description adds that it is a sector key discoverable via yahoo_finance_sectors, which is mildly useful, but adds no format, syntax, or validation detail beyond the schema. Baseline 3 is correct when schema does the heavy lifting.

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 (Fetch) and resource (Yahoo Finance details for one sector key), and explicitly distinguishes itself from the sibling discovery tool by scoping to a single key. An agent can tell it apart from yahoo_finance_sectors without opening either schema.

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?

Explicitly names the prerequisite alternative: 'Use yahoo_finance_sectors to discover available sector keys first.' This gives clear context for when to use this tool, though it does not state when-not to use it or contrast with yahoo_finance_industry.

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