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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered; the description adds meaningful provenance by explaining the APYs come from on-chain exchange-rate changes rather than advertised rates, which tells the agent these are realized, backward-looking figures. It does not disclose refresh cadence or whether exchange rates themselves are returned in the free tier.

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 compact sentences, front-loaded with the FREE qualifier that is the tool's main decision-relevant attribute. Every sentence carries information: cost tier, scope, data source, and the paid alternative.

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 zero parameters and no output schema, the description adequately conveys what an agent gets (3 top APYs, a subset of the 8 tracked assets) and its relative limits versus the paid sibling. Minor gaps remain on freshness and on exactly which fields the free response includes.

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 no parameters, so there is nothing to disambiguate and the baseline applies. The description correctly implies no filtering or configuration options exist.

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?

States a specific resource and scope: top 3 liquid-staking and yield-bearing stablecoin APYs, with concrete examples (stETH, rETH, sUSDe) and the derivation source. It also names the paid sibling staking_yields and what that returns, so an agent can tell the two apart 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?

The cost/completeness tradeoff against staking_yields ($0.005, 8 assets, TVL, exchange rates) is clearly conveyed, which effectively tells the agent when this free variant suffices. It stops short of an explicit 'use this instead when...' instruction and frames the alternative as a paid upsell rather than neutral routing guidance.

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