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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the exact price ($0.05 USDC via x402), the two-step protocol (calling returns the HTTP request and x402 payment requirements, then you pay with an x402 client), and the batch ceiling. Cost and payment mechanics are precisely the behavioral facts an agent needs before invoking.

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?

Three tight sentences, front-loaded with the cost and scope, then the returned fields, then the payment mechanics. No filler and every clause carries information.

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?

There is no output schema, so the description compensates by enumerating the returned fields, and it fully explains the payment gate that stands between the call and the data. Nothing an agent needs to invoke and interpret this tool 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 coverage is 100% for the single 'urls' parameter, so the schema already documents format ('comma-separated absolute URLs, max 20'). The description's 'up to 20 URLs' merely restates that limit without adding syntax or validation detail. 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 (check URLs), the batch limit (up to 20), and enumerates exactly what is returned (status, final URL, redirect count, latency, content-type, ok flag). It does not, however, differentiate itself from close siblings like page_check or robots_check, so an agent must infer the distinction from the return fields.

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?

Usage is implied by the batch scope ('check up to 20 URLs in one call') and the payment flow is described, but there is no explicit when-to-use vs. alternative guidance and no exclusions relative to the many sibling checkers.

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