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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description goes well beyond them: pay-per-call at $0.01 via x402 on Base, the x-credit-token prepaid header for unlimited calls, 1 free call/day per tool, and no API key requirement. Payment and auth requirements are exactly the kind of behavior an agent needs before invoking a paid endpoint.

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?

Purpose and scope are front-loaded before the sibling contrast, then payment details, which is a sensible order for a paid tool. It is somewhat padded by pricing/legal boilerplate ('Not financial advice', restating the limit ceiling), but no sentence is seriously misleading or wasted.

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 a full output schema, complete annotations and 100% parameter coverage, the description only needs to supply scope, routing and payment context — all of which are present. Nothing required to call the tool correctly is missing.

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 description coverage is 100%, and the schema already documents defaults (usd, 20) and the max of 100. The description adds only an example list of quote currencies (usd/eur/…) and repeats the limit ceiling; value over the schema is marginal, so the baseline 3 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?

States a specific verb and resource with fields: ranking top coins by market cap with price, mcap, 24h change and volume. It also explicitly separates itself from the sibling price tools ('our other price tools are Base-token-address based; this is the whole market'), so an agent can tell it apart from token_price/multi_price without opening schemas.

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?

Gives a clear consumption context ('the global snapshot an agent reads before trading') and an explicit contrast against the address-based price tools. It does not, however, distinguish from close siblings like crypto_global or crypto_trending, which also return market-wide data, so the routing guidance is clear but not exhaustive.

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