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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond that: end-of-day rather than real-time data, the covered universe (US large/mid caps, major foreign stocks, US ETFs), and the concrete metric set returned. No auth or rate-limit detail, which is the only remaining gap.

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 tight sentences that front-load the trigger condition, then the return payload, then the data-scope caveat. Every clause carries information an agent needs (count range, metric list, chart horizons, data freshness, exclusions); nothing is 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 single-parameter, read-only comparison tool with an output schema, the description supplies everything the schema and annotations do not: when to reach for it, what it returns, how fresh the data is, and what universe it covers. No material gap remains for correct invocation.

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% for the single parameter, which already documents the ticker format (AAPL, VOO, BRK.B), the 2-5 min/maxItems bounds and ordering. The description's '2 to 5 US stocks or ETFs' restates the schema bounds and only adds the US-listing scope restriction, so the baseline of 3 is appropriate.

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?

Names a specific verb (compare) and resource (2-5 US stocks or ETFs) and enumerates the exact outputs: returns, drawdown, Sharpe, beta, correlation and an overlaid 1Y/5Y chart. The scope limits ('End-of-day data', 'Not for intraday quotes') let an agent separate it from get_security_metrics and screen_securities without opening a 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?

Explicit trigger condition ('when the user wants to compare 2 to 5 ... side by side') with sample user phrasings, plus a clear exclusion ('Not for intraday quotes or recommendations on what to buy'). It does not name the sibling alternatives (get_security_metrics, screen_securities) for single-security or screening cases, so the routing guidance is clear but not fully closed.

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