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

Annotations already indicate readOnly, idempotent, and non-destructive behavior. The description adds valuable behavioral detail beyond that, including the $0.008 USDC cost via x402, the payment-challenge response for unpaid calls, the no-settlement-when-no-data rule, and the null-never-zero APY convention. This is strong transparency for a paid API.

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?

The description is front-loaded with the core purpose and filters, then covers output fields, use case, APY null semantics, cost/payment behavior, and an HTTP equivalent. Every sentence adds useful information without padding or repetition.

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?

Despite having no output schema, the description lists the returned fields (pool_id, chain, project, symbol, TVL, APYs, IL risk, exposure). It also covers payment behavior and the no-data cost rule, making it complete enough for an agent to invoke the tool and interpret results correctly.

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 input schema already documents all six parameters at 100% coverage, so the schema carries the parameter definition burden. The description reinforces the filter categories (chain, project, symbol, min TVL, stablecoin-only) and adds the ranking-by-APY context, but it does not add much meaning 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 specific action ('Screen DefiLlama's yield-pool universe') with explicit filters and output fields, so an agent knows exactly what the tool does. It is clearly distinct from siblings like defi_protocols or defi_chains because it focuses on yield pools and APY ranking.

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 provides a clear use case: 'Use it to find where a given asset earns yield.' It does not explicitly name alternative tools or give when-not-to-use guidance, but the context is specific enough for an agent to select it appropriately among the siblings.

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