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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world behavior. The description adds useful behavioral context: end-of-day rather than intraday data, the coverage universe (US large/mid caps, major foreign stocks, US ETFs), and a chart output. It does not cover auth or rate limits, so 4 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?

Three well-structured sentences: the usage condition is front-loaded, the metric list follows, and the scope exclusions close. Every clause earns its place with no repetition or 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?

An output schema exists, so return values need not be explained, and annotations already cover the safety profile. The description supplies the remaining needed context: when to use it, what metrics it returns, data timeliness, and excluded use cases. Nothing essential is missing for a single-ticker metrics tool.

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?

There is one parameter with 100% schema description coverage. The schema already documents the ticker format and examples, and the description adds no further syntax or format detail. The baseline of 3 applies when the 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?

The description states a specific verb+resource: retrieving performance and risk metrics for a single US stock or ETF. It lists the exact metric families (returns, drawdown, Sharpe, Sortino, beta, alpha) and scopes the coverage universe, which clearly distinguishes it from compare, screen, and backtest siblings.

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 gives an explicit when-to-use condition ('when the user asks how a single US stock or ETF has performed or how risky it is') and clear when-not exclusions ('Not for intraday quotes, news, earnings, fundamentals or price targets'). It does not name sibling tools as alternatives, so it falls short of a 5.

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