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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely non-obvious behavioral context: access-tier gating on history depth and, critically, the inverted scale ('LOWER IS HEALTHIER', 'a rising score means conditions are deteriorating'), which prevents a costly misinterpretation. It does not say what happens when `days` exceeds the free-tier cap (error vs. truncation), which is the remaining behavioral gap.

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?

Three sentences, front-loaded with what is returned, then limits, then score interpretation. Every sentence carries information an agent needs; the scale explanation is essential rather than padding because the polarity is counterintuitive.

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 does supply the return shape (one score plus regime per day) and the semantics of the values, which is sufficient for correct interpretation. The one omission is edge-case behavior when the requested window exceeds the account tier's limit.

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% and the schema already documents default 30 / max 3650, so the bar is baseline 3. The description earns above baseline by binding the `days` value to an access-tier constraint (31 free, 3650 premium), adding meaning the schema does not carry.

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?

States a specific verb+resource ('Daily Zensei Index scores ... with the regime of each day') for a bounded lookback window, which is clearly distinct from siblings like zensei_index_today and zensei_index_summary. It never explicitly names those siblings as alternatives, so differentiation is inferable rather than stated.

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?

Usage context is implied by the tier limits ('Free access covers the last 31 days; Premium covers up to 3650 days'), which tells an agent what range is obtainable. There is no explicit when-to-use-this-vs-another statement or exclusion relative to zensei_index_today / zensei_index_summary.

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