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

With readOnlyHint=true annotation, the description need not state read-only behavior. It adds valuable context: update frequency ('Updates: daily'), the percentile-ranking methodology, and the output field names. This goes beyond the annotation by explaining what the returned score represents and when it is current.

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 two sentences: the first packs the core functionality and output fields, the second provides usage guidance. No wasted words, and the essential information is front-loaded. This is an example of efficient, well-structured description.

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 there is no output schema, the description compensates by enumerating output fields (trend, confidence, top_drivers, realized_vol_20d_ann, vol_slope_10d) and detailing the score's construction. It also covers update frequency and use cases. It doesn't define each field's semantics, but for a read-only data tool with a single optional parameter, this is sufficient.

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 single 'days' parameter is already fully described in the input schema. The tool description does not add parameter-level detail, which matches the baseline of 3 as the schema carries the burden.

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 the tool returns a daily 0-100 volatility regime-shift score with specific calculation methodology (10-day OLS slope of SPY 20-day realized volatility, percentile-ranked against 252-day history). It lists the output fields, making the resource and intended data highly specific and distinct 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?

Explicitly provides when-to-use conditions: 'Call when the user asks about volatility regimes, vol expansion or compression, whether market volatility is rising or falling, or SPY realized vol trend, or when timing entries, exits, hedges, or long/short-gamma options positioning.' However, it does not mention alternatives or exclusions, so it falls short of a full 5.

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