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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the paid x402 model ($0.002 USDC per successful call across Base/Solana/Arc), that failed calls are free, the upstream data source, the exact per-pool fields returned, and a caveat about missing audit data. This is exactly the extra behavioral context a paid read tool needs.

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 sentences, each carrying distinct payload: what it ranks and returns, what it deliberately cannot tell you, and what it costs. The most decision-relevant fact (APY ranking, not safety) is placed prominently before the price detail.

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?

Given an existing output schema, the description still summarizes returned fields, and it covers the two things structured fields cannot: the upstream data source's limitations and the payment/billing behavior. Nothing an agent needs in order to call it correctly or explain the charge 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 description coverage is 100%, so the schema already documents all five parameters including defaults for chain, limit, maxApyPct and minTvlUsd. The description restates the filtering dimensions but adds no syntax or format guidance beyond the schema, so 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?

States a specific verb and resource ('Ranks DeFi pools by total APY'), names the underlying source (DefiLlama public yields), and enumerates the output fields. An agent can distinguish it from neighbors like dex_depth_slippage_calculator or stablecoin_peg_integrity_radar without opening the 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 description establishes scope ('filtered by chain, minimum TVL and optional stablecoin-only') and a clear exclusion ('Ranking is by APY, not by safety: there is no audit or exploit-history score'), which is a meaningful when-not-to-rely signal. However, it never names an alternative tool to use for safety/audit questions, so routing is left to inference.

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