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

Annotations provide readOnlyHint=true and openWorldHint=false, covering the safety profile. The description adds value beyond annotations by disclosing the update frequency ('Updates: daily'), the underlying methodology (60-day rolling z-score, CUSUM, Shannon entropy), and the data history (9+ years). It does not contradict annotations, and no major behavioral traits are obscured.

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 information-dense but compact. It front-loads the score definition and output fields, then gives usage triggers, and finally the update cadence. Every sentence contributes meaningful information without redundancy or fluff.

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?

The tool has no output schema, but the description lists all return fields (trend, confidence, top_drivers, ewc_raw, cusum_statistic) and the score range (0-100). It also explains the methodology and when to use it. However, it does not interpret the score direction (e.g., higher = higher risk), which is a minor gap given the lack of an output schema.

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 description coverage is 100% for the only parameter 'days', which already includes a detailed description including the Gold tier requirement and fallback behavior. The tool description itself does not add any additional parameter semantics. Per the baseline for high schema coverage, a 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 the tool returns a 0-100 volatility regime-shift early-warning score for US equities, with specific methodology (SPY log-returns, rolling z-score, CUSUM, Shannon entropy). It lists all output fields (trend, confidence, top_drivers, ewc_raw, cusum_statistic), making its purpose unmistakable. Even among many sibling tools, the specific asset class (US equities) and output distinguish it.

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 says 'Call when the user asks about market volatility, regime change, S&P 500 instability, turbulence, or vol spikes, or when timing position sizing, hedge adjustments, or options/straddle exposure ahead of market instability.' This gives clear when-to-use triggers. However, it does not mention alternatives or exclusions, so it does not fully differentiate against sibling tools that might also handle volatility signals.

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