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

Annotations already provide readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, establishing a safe read-only profile. The description adds valuable behavioral context: the index source (DVOL), the interpretation of percentile context, the square-root-of-time scaling for expected moves, and the fallback behavior for unsupported coins. There is 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 is front-loaded with the core purpose and has a logical flow: purpose → outputs → interpretation caveats → sibling differentiation → constraints. However, it is somewhat verbose, especially the detailed square-root-of-time explanation and the example about percentiles. While this adds educational value, it makes the description longer than strictly necessary for tool selection. Still, it remains well-structured and informative.

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 that an output schema exists (indicated true), the description does not need to detail the return format. It adequately covers the tool's outputs (30-day IV, percentile stats, expected moves), explains critical interpretation points (annualized percent, percentile context, time scaling), and handles edge cases (unsupported coins). The agent can fully understand the tool's role and behavior without additional context.

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%, so the baseline is 3. The description adds extra meaning beyond the schema by clarifying that the 'coins' parameter only works for BTC/ETH and that other values result in an 'unavailable' response rather than an error. While it doesn't elaborate on windowDays beyond what the schema says, this additional behavioral detail for the coins parameter is valuable and justifies a score of 4.

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 states it returns options-implied volatility (DVOL index) and expected moves, using specific verbs ('prices how expensive protection is'). It explicitly distinguishes itself from sibling derivatives tools that describe market positioning and from get_macro_rates (VIX for US equities). The purpose is unambiguous and specific.

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 tells when to use this tool (to get crypto implied volatility) and when not: 'Every other derivatives tool here describes how the market is POSITIONED; this one prices how expensive protection is.' It contrasts with get_macro_rates for VIX and notes that only BTC and ETH are supported, with non-supported coins returning 'unavailable' rather than failing. No alternative usage guidance is missing.

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