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

Annotations only cover readOnly/openWorld; the description adds materially more: no API key required, per-call cost of $0.002 USDC via x402 on Base/Solana/Arc, and that failed calls are not charged. That payment/auth behavior is exactly the operational context 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?

Dense but front-loaded: the resource and return shape come first, then access model, then pricing. Every clause carries distinct information — no filler, no restatement of the title.

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?

Only two parameters, both fully documented, an output schema exists, annotations cover safety, and the description supplies the pricing/payment and no-key details that annotations cannot. Nothing an agent needs to invoke it 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%, with both `url` and `limit` documented inline including accepted forms and the 1–50 default range. The description merely restates that a URL or domain can be looked up, adding no format or edge-case detail beyond the schema, so 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 the specific verb and resource: the Internet Archive Wayback Machine CDX index, returning archived snapshots. It enumerates the returned fields (timestamp, original URL, MIME type, HTTP status, length) and explicitly scopes out page text, so an agent can separate it from content-extraction or news-search siblings.

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 clear context for use (historical capture lookups for a URL or domain) and a negative constraint — 'the index lists captures, not page text' — which steers agents needing page content elsewhere. It stops short of naming an alternative tool explicitly, so it falls short of a 5.

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