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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive behavior. The description adds the non-obvious paywall behavior: 'Returns HTTP 402 until the MCP client supplies a valid payment for this call.' This is meaningful context beyond the annotations, though the payment mechanics are not detailed.

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?

Two sentences with no filler; the operational 402 behavior is stated crisply. The first sentence is a dense list but still readable and front-loaded.

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?

The description covers core purpose and the critical paywall behavior, and the output schema/annotations carry return and safety information. However, it lacks usage guidance and parameter explanations, so it is not fully complete for selecting and invoking the tool correctly.

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 only 25% (only resource_url is described), and the description does not clarify method, max_price_usd, or expected_network. The audit-scope list does not map to these parameters, so the low coverage is not compensated.

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?

The description specifies a concrete action (purchase/audit) on a named resource (x402 endpoint) and enumerates the audited areas: payment schema, discovery metadata, redirects, CORS, cache, and operational signals. However, it does not explicitly contrast with inspect_x402_endpoint or order_x402_remediation, so sibling differentiation is left implicit.

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?

No guidance is given for when to prefer audit_x402_endpoint over inspect_x402_endpoint or order_x402_remediation. The only usage-related note is the payment gating condition, which is operational rather than a selection criterion.

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