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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description adds genuinely new behavioral context beyond them: the exact return payload (series by expiration, spot, overall ATM IV) and the free/pro ticker access restriction, which is a hard constraint an agent needs when selecting the tool.

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?

Front-loaded with what the tool returns, then use cases, then access tiers; each sentence carries information. The ticker enumeration is long but functionally necessary for the access constraint, so it stays efficient rather than padding.

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 naming the returned components (IV by expiration, spot, overall ATM IV), and annotations carry the safety profile. The only gap is that it does not distinguish itself from the contract-level vol siblings, so it is complete but not maximally informative.

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 100% for the single ticker parameter, so the schema already documents the argument fully. The description adds no syntax or format detail beyond it (the examples are just illustrative tickers), so the baseline 3 applies.

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 names a specific resource and its scope: ATM implied volatility by expiration (the IV term structure), plus spot and the overall ATM IV for a ticker. An agent can tell this is a vol-curve tool rather than a chain or single-contract tool. It stops short of explicitly contrasting with the nearest sibling (contract_atm), which keeps it at 4 rather than 5.

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 concrete when-to-use signals via example questions ('is NVDA implied volatility elevated?', 'is the vol curve inverted before earnings?'), which is clear context. It does not name a when-not condition or point to alternative tools, so it is clear-but-incomplete rather than fully routing.

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