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

With no annotations provided, the description fully discloses behavioral traits: it uses no target credential/signature/payment, follows no redirects, never reads the paid target body, and only reads a same-origin public OpenAPI document under a strict size cap. It also clearly warns that seller declarations are advisory and not proof of validity/trust/reliability.

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?

Though dense, every sentence carries critical information: purpose, usage contrast, safe-operation boundary, and advisory nature. It is front-loaded with the core action and then systematically covers constraints. No fluff or repetition.

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 is fully sufficient for an agent to understand the tool's scope, limitations, and input expectations. It addresses all key aspects: exact route requirement, comparison dimensions, safety guarantees, and the advisory nature of results. The presence of an output schema further reduces the need to explain return values, and the description still outlines what evidence is gathered.

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%, and the description adds substantial meaning beyond the schema. For the url parameter, it explains that the route's unpaid challenge headers and OpenAPI declaration will be inspected. For the catalog parameter, it details exactly how the comparison is performed (across request, protocol, amount, network, asset, recipient, and expiry). This goes well beyond the raw schema descriptions.

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 states a specific verb ('Compare') and resource ('x402 and MPP payment challenges, terms, and seller-declared JSON success-response readiness') for a precise target (one exact public HTTPS GET route). It clearly distinguishes itself from siblings by explicitly naming agent_discoverability_audit as the alternative when catalog ranking/exposure is needed.

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?

The description explicitly states when to use this tool ('before buyer authorization'), what it covers (URL/realm binding, expiry, parity, OpenAPI evidence), and when not to use it (explicitly directing to agent_discoverability_audit for the alternative use case). It also clarifies what the tool does not do (no credentials, no redirects, no reading paid body).

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