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

readOnlyHint=true and openWorldHint=false already establish the safety profile, so the description adds real value beyond annotations: it flags the free tier, the fixed top-5 result cap, and the cost of the paid filtering path. It doesn't describe the shape of a returned yield entry, but the ranked-APY framing and the fixed cap cover most operational expectations.

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?

Three short sentences, with the most decision-relevant fact (FREE) front-loaded. Every sentence earns its place: what it returns, how it is ranked, and where to go for filtering.

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 parameterless, read-only, no-output-schema tool, the description adequately conveys the bounded result set (top 5, ranked) and the escape hatch for richer queries. Only the exact fields of each yield entry are unspecified, a minor gap for a simple ranked list.

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 tool takes zero parameters, so the baseline is 4 and there is no parameter syntax for the description to clarify. It correctly signals parameterlessness by directing any filtering need to lookup_yields.

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 states a specific verb, resource, and scope: the top 5 DeFi yields ranked by risk-adjusted APY. It explicitly distinguishes itself from the sibling tool lookup_yields by noting it is the free, unfiltered counterpart. An agent can route between the two without opening either schema.

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?

It names the alternative (lookup_yields) and the exact condition that selects it: filtering by chain/token. The price of the alternative ($0.003) is included so the agent can weigh cost. This is explicit when-to-use-this-vs-that guidance.

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