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

With no annotations, the description carries the full behavioral burden. It usefully discloses a concrete cost of 0.001 USDC per call via x402 and implies a read-only data lookup, but it does not describe the first-call 402 payment handshake, rate limits, caching, or error behavior. The payment proof schema covers the handshake mechanics, so the description's cost disclosure is meaningful but incomplete.

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?

Two short sentences with zero filler. The primary capability is front-loaded, followed by the payment cost, making the definition easy to scan.

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?

For a simple read-only data tool, the description covers the core return values and payment cost. However, with no output schema and no annotations, it leaves gaps around the days parameter limits, payment flow behavior, and response format details that would help an agent invoke it confidently.

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 only 50%: paymentProof is well documented in the schema, while days has no schema description. The description says 'previous days for trend,' which hints that days controls lookback, but it does not mention the parameter name, default of 7, or maximum of 30, so it does not compensate for the undocumented half of the parameters.

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 resource and returned content: the current 0-100 crypto Fear & Greed index, its classification, and previous days for trend. It is readily distinguishable from sibling tools like crypto_price or technical_indicators, though it does not explicitly name or contrast those alternatives.

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 explains what data is returned but gives no guidance on when to use this tool versus alternatives. There are no exclusions, prerequisites, or named sibling tools to help an agent route between this and related crypto data tools.

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