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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, making the tool's safety profile clear. The description adds valuable context about 'immutable daily history' and the existence of CeFi/DeFi splits and TVL weighting, which go beyond annotations without contradicting them.

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?

Two sentences, no filler. The first sentence defines the tool's output precisely; the second gives targeted usage guidance. Every word earns its place. Front-loaded structure makes it easy to scan.

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 read-only index tool with decent annotations and an output schema, the description covers the core behavior: segments, TVL-weighted variant, deltas, history immutability, and access clamping. Minor omission: 'deltas' are mentioned but not defined, though likely detailed in the output schema. Overall sufficient for selection and invocation.

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 coverage is 100%, providing baseline meaning. The description adds extra semantic value by explaining the effect of omitting the segment parameter ('headline across overall + CeFi + DeFi') and the access clamp on history_days ('anonymous/free access is clamped to the most recent 90 days'), which are not evident from the schema alone.

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 clearly states the tool returns the median USDC/USDT lending APY across servable providers, with splits and history. It uses specific verbs ('median', 'TVL-weighted', 'immutable daily history') and distinguishes itself from a single provider quote, making it unambiguous among siblings like stablecoin_index or list_earn_products.

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 explicit use cases ('what does stablecoin yield pay right now / how has it trended?') and clarifies it is a citable market reference rather than a single provider quote. However, it does not directly name sibling alternatives like stablecoin_index or list_earn_products to exclude them, leaving some differentiation implicit.

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