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

The description provides substantial behavioral detail beyond the readOnlyHint: it explains the calculation methodology (WTI log-return stdev 70% + Energy CPI stdev 30%), data source (FRED), update frequency (monthly), output fields, and optional history mode with Gold tier requirement. No contradiction with annotations.

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 packs a lot of useful information into a single dense sentence followed by a short 'Updates: monthly.' While not perfectly structured, it contains no fluff and front-loads the core purpose before usage guidance.

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?

Given the tool's moderate complexity and lack of an output schema, the description is remarkably complete: it explains the index formula, output fields, usage scenarios, update frequency, and the optional history mode with tier restrictions. An agent can accurately decide when and how to invoke this 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?

The only parameter, 'days', is fully documented in the schema with details about optional history series, bounds, and Gold tier requirement. The description does not add parameter-specific information beyond what the schema already provides, but since schema coverage is 100%, 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?

The description uses a specific verb ('Returns') and identifies a precise resource: a 0-100 energy-cost volatility index with a clear formula and data source. It also lists the output fields, making the tool's purpose unmistakable and distinguishing it from generic sibling tools.

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?

The description explicitly states when to call the tool ('Call when the user asks about energy price risk, oil/fuel cost swings, or hedging energy exposure...) and gives concrete use cases like timing energy contract locks and WTI futures hedges. It does not mention when not to use it or alternatives, so it falls just 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.