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

Annotations cover only readOnly and openWorld, so the description carries the important extras itself: a per-call cost of $0.002 USDC, the x402 payment rails (Base, Solana, Arc), and the crucial detail that failed calls are not charged. That cost-and-failure policy is genuinely decision-relevant for an agent, though rate limits or data freshness/lag are not mentioned.

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 capability is stated first, followed by attribution, disclaimer, and pricing — a sensible front-loading order. The pricing sentence is dense with parenthetical payment rails but every clause (attribution, non-advice, price, free-on-failure) carries distinct information.

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 an output schema present, return values need not be explained, and the billing model—the main risk for an autonomous caller—is fully disclosed. Coverage is solid for a one-parameter read tool; only freshness/latency and sibling disambiguation are missing.

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% and the single 'days' parameter is fully documented as '1 to 30 days (default 1)'. The description only restates the upper bound ('up to 30'), adding no format or edge-case detail beyond the schema, so the baseline 3 applies.

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 names a specific resource (the Crypto Fear & Greed Index) with a clear scope ('today and for the previous days, up to 30') and output content (classification from extreme fear to extreme greed). It does not distinguish itself from nearby siblings like crypto_indicators or sentiment, which likely also return market sentiment-style data.

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 only implied: an agent can infer this is the tool for historical fear/greed readings, but there is no statement of when to prefer it over crypto_indicators, sentiment, or macro readings, and no exclusions. The remaining sentences cover attribution, disclaimer, and billing rather than selection guidance.

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