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

With no annotations at all, the description carries the full burden and does well: it discloses the paid model, the exact price and accepted payment chains, that failures are not charged, and that no account/API key is needed. Unstated are the response shape, freshness/caching, and how payment is settled per call, which is why it is not 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?

All substance fits in two dense sentences, and the most decision-relevant fact ('Paid') is front-loaded ahead of the data contents. The telegraphic style is efficient, though the middle clause list is slightly run-on.

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 parameterless, annotation-free data fetch with no output schema, the description compensates by enumerating the returned metrics, naming the data provider, and spelling out cost and payment mechanics. It is sufficient to call correctly; only freshness and response format remain unspecified.

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, so there is nothing for the description to disambiguate beyond what the empty schema shows. Baseline for a no-parameter tool 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?

The description names the specific resource (Sky Dollar / USDS) and enumerates exactly what the call returns: price vs peg, supply, 1d/7d/30d supply change, and per-chain supply. That distinguishes it from sibling buy_stable_* tools keyed to other stablecoins. The action verb is only implied ('live'), so it stops short of a crisp verb+resource statement.

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 useful context (data source DefiLlama, paid at $0.01 USDC, no account or API key) that tells an agent this is a paid data pull. However, it never says when to choose this over neighbours like buy_yields_token_usds, buy_stable_usdc, or buy_crypto_price, and has no explicit when-not-to-use guidance.

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