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

Annotations already establish read-only, open-world, non-destructive behavior. The description adds genuinely new operational context: the per-call cost, that payment is via x402 with USDC on Base, and that failed calls are not charged — an agent-relevant billing/authorization detail. It does not explain why the tool is flagged non-idempotent (presumably live changing data), leaving that one hint unaddressed.

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 sentences, zero filler: what it returns first, commercial terms second. Every clause carries information the agent cannot get from schema or annotations.

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 return-value burden and does so by naming the data components returned. It omits shape/format detail (e.g., whether the index is 0-100, how 'mood' and 'volatility regime' are expressed), but an agent can call it correctly with what is given.

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 optional 'limit' parameter is fully documented in the schema at 100% coverage, including its 1-7 range and default. The description adds no meaning beyond that, which is acceptable given the schema does the work, but it does not connect 'trending coins' in the description to the limit parameter.

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 enumerates the concrete payload: Fear and Greed index with prior value, trending coins, market breadth, mood, and volatility regime. That is far more specific than the bare name 'sentiment'. It does not, however, distinguish itself from sentiment_free, which is the most likely source of confusion among siblings.

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 by the pricing statement (USD 0.003 per call, x402/USDC on Base), which hints this is the premium tier and that a free alternative exists. There is no explicit 'use this when...' or 'use sentiment_free instead when...' guidance, so the agent must infer the trade-off.

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