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

Annotations include readOnlyHint=true, so safety is disclosed. The description adds valuable behavioral context: the exact computation definition (spread as VIX minus SPX RV20d) and that it returns an interpretation. This goes beyond simple read-only labeling, though it doesn't address data freshness or limitations, which would warrant a 5.

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?

Two dense sentences, front-loaded with the core output and followed by specific use cases. No wasted words; jargon is appropriate for the domain. The structure efficiently communicates purpose and applicability.

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?

No output schema exists, so the description must explain return values; it does (label, spread, ratio, interpretation). It also covers typical use cases. It doesn't mention data history or as-of date, but for a state-style snapshot tool, this is not a critical gap. Overall well-rounded for its complexity.

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 for parameters is 100% (apiKey is fully described). The tool description adds nothing about parameters, but since the only parameter is a well-documented API key, the schema carries the burden effectively. A 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 clearly specifies the tool's output: a VIX regime label (overvixing/undervixing/neutral), spread (VIX minus SPX RV20d), ratio, and interpretation. It uses a specific resource ('VIX regime state') and distinguishes it from sibling tools like get_realized_vol or get_vrp by focusing on the VIX-vs-realized-vol comparison.

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?

Explicitly lists use cases: 'classify fear gauge premium, identify contango/backwardation..., time volatility-selling strategies.' This gives clear context for when to invoke the tool. However, it does not name alternative tools or provide when-not-to-use guidance, so it falls short of the highest bar.

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