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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is fully covered. The description adds value by enumerating the exact payload (index, band, historical comparison points), which is the main behavioral fact an agent needs given there is no output schema.

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?

One sentence, zero waste, front-loaded with the resource and its value range. Every clause conveys distinct information about the returned fields.

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 carries the burden of explaining return values and does so precisely. Minor residual ambiguity: it is unclear whether the '30 days ago' figure is always present or only when `historico=1` is set, since the description lists both 7- and 30-day values unconditionally.

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 single parameter `historico` is fully documented in the schema, including its enum value and effect ('With 1, also the last 30 days'). Schema coverage is 100%, so the baseline of 3 applies; the description adds no additional parameter meaning and does not note that the parameter is optional.

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 the exact resource (today's crypto fear and greed index), the value range (0-100), and the companion fields returned (band, yesterday, 7 and 30 days ago). An agent immediately knows what data this yields. No sibling differentiation, but the sibling list is unrelated analytics tools, so confusion risk is low.

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 is implied rather than stated: this is clearly a point-lookup for market sentiment. There is no explicit 'use this when...' guidance, no mention of alternatives, and no note on freshness/caching. For a simple read-only lookup tool, implicit usage is largely adequate.

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