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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds meaningful behavioral detail: it returns 'each trading day's close WITH the previous close and the computed daily return percent, per symbol' and notes it is 'Keyless (Yahoo Finance).' This goes beyond the annotations, though it stops short of discussing edge cases like holidays or weekends.

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 dense but well-structured and front-loaded with the key intent. Every sentence provides essential information—use case, symbol types, return content, and distinction from get_quotes—without fluff.

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?

With no output schema, the description compensates by explaining the returned data: 'close WITH the previous close and the computed daily return percent, per symbol.' It also covers the full parameter set, symbol universe, keyless access, and the distinction from current-price tools, making the tool fully understandable.

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%, providing baseline 3, but the description adds value by expanding the symbol semantics: 'same symbol space as get_quotes' and listing categories such as indices, commodities, crypto, and FX. It also reinforces date range behavior with examples, which helps the agent use params correctly.

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 clearly identifies the tool's purpose: 'PREFER for HISTORICAL closing prices and daily returns on a specific past date or date range.' It explicitly contrasts with get_quotes and includes concrete examples, making it unmistakable what resource and verb are involved.

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?

Usage guidance is explicit and actionable: 'Use get_quotes for CURRENT prices; this tool is for any date in the past.' It also states when the tool should be preferred and provides the symbol space context, clearly steering the agent away from inappropriate use.

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