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

Goes far beyond the readOnly/destructive annotations: https-only, 5 s timeout, 64 KB cap, no redirects, body never returned on non-402, exact error code not_x402_resource, and rate limits (20/min per IP keyless, key limits otherwise). These are precisely the operational constraints an agent needs before calling.

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?

One dense paragraph, front-loaded with the core action, then limits, then return/error behavior, then auth and rate limits. Every clause carries a distinct constraint; nothing is repeated from the annotations.

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?

No output schema exists, and the description compensates fully by specifying what a 402 returns (parsed payment requirements from PAYMENT-REQUIRED header or accepts[]) and what every other status yields. Nothing needed to call or interpret the result 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% and the single parameter is already documented as a full https:// URL. The description reinforces the https-only constraint and that the target must be an x402-paid endpoint, adding modest but real meaning over the schema.

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 ('Probe one x402 resource URL without paying') plus the exact mechanics (single GET). The 'without paying' qualifier implicitly separates it from bazaar_pay_and_call and it reads as a follow-up to bazaar_discover_resources, so an agent can place it in the workflow without opening a schema.

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?

Clearly frames the use case (inspect an endpoint's payment requirements before committing to a paid call) and rules out prerequisites ('No signing. No API key needed'). It never names bazaar_pay_and_call explicitly as the escalation path, so the alternative is inferable rather than stated.

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