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

Annotations already mark the tool as read-only; the description adds valuable context about data source (Stooq OHLCV, daily since 2016), update frequency ('Updates: daily'), and expected output fields, going beyond the annotation baseline.

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 composed of two substantive sentences plus a brief update note. It is front-loaded with the core result, then use cases, and ends with cadence—every sentence earns its place with no redundancy.

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 read-only tool with a single optional parameter and no output schema, the description covers the return fields, data source, update cadence, and use cases. The schema handles parameter semantics and tier limitation, making the overall context complete.

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 input schema with a rich description covering history behavior and Gold tier requirement. The main description does not add parameter details, but since schema coverage is 100%, the baseline of 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 clearly states a specific verb ('Returns') and resource ('a 0-100 volatility-regime score for SPY') with a detailed methodological definition. It also lists output fields, distinguishing this from sibling tools as a volatility/tail-risk indicator.

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 provides explicit use cases ('Call when the user asks about volatility regimes, tail risk, market turbulence, vol spikes, or S&P 500 risk') and even tactical applications ('timing protective hedges, put spreads'). However, it does not name specific sibling alternatives or provide a when-not-to-use statement.

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