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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint as safe. The description adds valuable behavioral context: deep/report tiers perform 'unpaid 402 probing' when paid_path is supplied, which indicates active probing of a paid endpoint without making a payment. It also lists the discovery surfaces scanned, which is not present in 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?

The description is two well-structured sentences. It front-loads the core purpose, then lists key parameters and behavioral triggers. No filler, redundant information, or repetition of schema elements; every clause adds value.

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?

Given the existence of an output schema, the description appropriately focuses on selection and invocation context. It explains what the tool does, when deep/report tiers probe, which parameters matter, and the cost tiers. It is complete for an agent to decide when to use it and how to invoke it, especially with sibling tools available for alternative operations.

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?

Input schema covers all 7 parameters with descriptions (100% coverage), so the baseline is 3. The description adds extra meaning beyond the schema: it explains tier pricing ($1/$5/$10), the optional parameters to pass, and the relationship between tier and paid_path (deep/report tiers add unpaid probing). This semantic enrichment goes beyond the schema's bare definitions.

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 uses a specific verb ('check') and resource ('x402/agent-facing tool') and clearly states the purpose: readiness for agent routing, marketplace listing, and paid-path monitoring. It lists concrete discovery surfaces, and the surrounding sibling tools (probe_x402_paid_path, scan_x402_resource) make the differentiation clear.

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 gives clear context on when to use the tool: to check readiness for routing, listing, and monitoring. It also explains tier options and when deep/report tiers trigger unpaid 402 probing. It does not explicitly name alternatives or exclusions, but the sibling tool names and the phrase 'unpaid 402 probing' imply when this tool is the right gate versus actual probing tools.

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