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

With no annotations supplied, the description carries the full burden, and it does well: it discloses paid access ($0.005 USDC on Base or Solana), no account/API key required, and that failed calls are not charged — behavior an agent cannot get from the schema. It stops short of describing the response shape, row structure, or rate limits, which keeps it below a 5.

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?

Roughly four compact sentences, front-loaded with 'Paid.' and then the purpose, so the highest-risk fact hits first. Slight redundancy in restating the endpoint URL and the currency breakdown, but nothing needs to be cut to understand the tool.

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 three-optional-parameter read tool with no output schema and no annotations, the description covers what is queried, what fields come back (APY, TVL), the data provenance, and the payment model. The remaining gap is that it does not describe the per-row shape (pool, protocol, chain identifiers) or how many results a paid call covers.

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 all three parameters (sort, limit, min_tvl_usd) are already documented in the schema; that sets the baseline at 3. The description only glancingly touches these by naming APY and TVL, without adding default or range semantics beyond what the schema already provides.

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 concrete verb and resource — 'Where to earn yield on WBNB' with 'live pools holding WBNB across protocols and chains, APY and TVL' — and names the upstream data source (DefiLlama). 'Across protocols and chains' implicitly separates it from the chain-scoped buy_yields_chain_* siblings without naming them explicitly, which keeps it just short of a 5.

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 implied rather than stated: an agent can infer this is for token-scoped yield discovery, but there is no explicit when-to-use or when-not-to-use guidance and no named alternative (e.g. buy_yields_chain_bsc or buy_yields_protocol_*). The payment and access notes are billing context, not selection guidance.

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