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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description goes beyond them by disclosing the pricing model ($0.002 USDC per successful call via x402 on Base, Solana or Arc, failed calls not charged) and the data-scope limitation on collateralization. It does not describe freshness/lag of the yields figures, which keeps it short of 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?

Front-loaded with the data payload, then scope exclusion, then cost — a sensible order with no filler sentences. The detour naming crypto_kaspa_toccata_status consumes space without helping selection and briefly misleads before being dismissed as 'a different need'.

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 an output schema present, return values need not be described; the description still covers sources, chain, exclusions, and payment terms, which is enough to call it correctly. The one weak spot is that the irrelevant sibling reference leaves the intended alternative for overlapping indexer tools unstated.

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 zero parameters and its schema is fully covered, so there is nothing for the description to disambiguate. Baseline for a no-parameter tool is 4; no parameter meaning is added or needed.

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 names the exact resources returned — sUSDS/sDAI savings APY and TVL on Ethereum, DAI and USDS USD price, depeg %, and circulating supply — with sources (DefiLlama yields). Crucially it pre-empts the misleading tool name by stating that vault collateralization is not covered, so an agent knows the scope precisely.

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?

It gives one useful exclusion ('Vault collateralization is not in these sources and is not reported'), which tells an agent when not to use it. However, the explicit 'related tools' pointer routes to crypto_kaspa_toccata_status, which is unrelated to this data, while genuinely overlapping siblings like crypto_defillama_yields, crypto_defillama_stablecoins, or crypto_lido_steth_peg are never mentioned.

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