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

Annotations already cover readOnly, idempotent, non-destructive and open-world, so the bar is lower; the description nonetheless adds real context beyond them: pricing (free), the 365-day history cap, and error semantics (isError message on invalid input or upstream failure, not charged). It does not describe caching or refresh behaviour, but for a read-only public index this is solid.

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?

Front-loaded with the resource and scope, then cadence, source, limits, price, and error behaviour as compact clauses. Dense but every fragment carries information; the telegraphic style slightly hurts readability but wastes nothing.

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 description still covers source, cadence, history bound, cost, and failure behaviour. An agent has everything needed to call it correctly; only explicit alternative-routing guidance is 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 coverage is 100% and the single 'days' parameter is fully documented in the schema (range 1–365, default 30). The description's 'Up to 365 days of history' merely restates the schema bound rather than adding new meaning, 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?

Names a specific resource (Crypto Fear & Greed Index 0–100), states what is returned (current value plus history, 7d/30d average, extremity), and identifies the data source (alternative.me, daily). It is clearly distinguishable from market-price siblings like crypto_price or price_history.

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 source and daily cadence imply when this tool applies (sentiment readings, not price data), but there is no explicit when-to-use or when-not guidance and no sibling is named as an alternative. Usage must be inferred.

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