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

Annotation coverage is thin (readOnlyHint=false, openWorldHint=true), and the description more than compensates: it discloses the paid cost ($0.004 USDC), the two-phase x402 payment flow (quote call charges nothing, second call with signed payment settles), the data source (DefiLlama) with a no-advice disclaimer, and the no-zero-pricing edge case for stale coins. This is exactly the kind of context annotations cannot carry.

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 purpose, then guidance, then return shape, then payment mechanics, then disclaimer — a logical order with no padding sentences. It is slightly long, and the payment flow is repeated in both the body and the schema description, which keeps it from a 5.

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 an output schema, the description still summarizes the return shape (one row per coin with price, both changes, timestamp, pricing confidence, plus advance/decline counts) and covers the stale-coin edge case. For a paid, open-world tool with no destructive semantics this is complete enough for confident 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%, so baseline is 3; the description adds real meaning by framing payment_signature as a two-call workflow (omit to get the quote, include the signed payment to receive results) and by restating that coins accepts CoinGecko ids or major-coin tickers with a default of the twelve major coins. It stops short of adding new syntax beyond the schema, so it sits just above baseline.

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?

Names a specific verb+resource (single-call USD price with 24h and 7d change for major coins, or up to 25 named coins) and explicitly positions itself against siblings, routing single-coin and contract-address lookups to genesis402_catalog/genesis402_call. An agent can distinguish it from the other market/pricing tools without opening any schema.

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?

States the exact triggering condition ('use when you need more than one price at once: one payment instead of one per coin') and the exclusion (single coin or token by contract address → catalog + call). Both the when and the when-not are explicit, which is rare.

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