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

Annotations declare readOnlyHint=true, and the description aligns, describing a read-only calculation. It adds behavioral context beyond annotations: data source (SPY via Stooq), update frequency (daily), score range, and output fields, which set expectations for what the tool returns. No contradiction detected.

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 three concise sentences: what it returns, when to use, and update frequency. It is front-loaded with the main output and every sentence provides value without filler.

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 enumerates the return fields, which is crucial. It also provides methodology and use cases. The only minor omission is not explicitly stating it is a market-wide indicator (SPY proxy), but the description implies this via 'for US equities' and SPY. Sufficiently 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 schema with a description, constraints, and tier requirement. Schema description coverage is 100%, so the tool description does not need to add parameter details. 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 states it returns a 0-100 volatility-range expansion score for US equities, with specific methodology (ATR-14 vs ATR-252, percentile-ranked over 10 years) and a list of output fields. This is a specific verb+resource+scope that distinguishes it from generic market 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?

Explicitly states 'Call when the user asks about volatility expansion, widening trading ranges, ATR, or breakout setups' and also lists use cases like timing momentum entries and breakout alerts. This gives the agent clear, actionable triggers for invocation.

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