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

Annotations already establish read-only/idempotent/non-destructive, and the description adds a lot on top: exact price (0.01 USDC), the x402 payment path (USDC on Base or Solana, no account or API key), that invalid input is rejected before payment, failed runs are never charged, and that an unpaid call returns PaymentRequired. That is precisely the billing and failure behavior an agent cannot infer from annotations.

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 and front-loaded: coverage list first, then scoring output, then price/payment, then escape hatches. The trailing full HTTP URL with percent-encoding is slightly noisy for an MCP caller, but everything else earns its place.

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 one-parameter read-only tool with no output schema, the description still explains the return shape (0-100 scores per area with concrete fixes), the payment/error states, and a free-sample path. Nothing an agent needs before calling 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?

There is a single parameter with 100% schema description coverage, so the schema already carries the semantics. The description adds only an HTTP-form example URL with the query string; otherwise it does not explain accepted URL formats or domain normalization, so the baseline of 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?

Opens with a specific verb+resource ("Website audit in one call") and then enumerates exactly what is checked: TLS, security headers, redirects, HTTP/2/3, compression, SEO tags, AI-agent readiness. That enumeration also separates it from narrower siblings like url_safety_check, uptime_check, and broken_links, which each cover only one slice.

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?

"In one call" implies this replaces the per-check siblings when a full picture is wanted, and it explicitly routes to get_example for a free sample. It does not, however, state when to prefer url_safety_check or uptime_check instead, so the exclusions are left implicit.

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