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

Annotations already declare readOnlyHint=true and openWorldHint=true. The description goes beyond this by adding costs ($0.10 per call), experimental status (may change/withdrawn), and explicitly stating 'No payment is signed or submitted.' It also clarifies the scope (one public endpoint, anonymous caller). This adds meaningful behavioral context without contradicting the 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 a single, information-dense paragraph that front-loads the experimental warning, then states the action and output. It contains no fluff—every clause earns its place (e.g., the cost, the no-payment note). It could be split into clearer bullet points, but it's efficient and readable.

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 tool has only one parameter and no output schema, so the description bears full responsibility for explaining the return value. It enumerates the exact components of the report (status, rails, headers, health checklist) and adds cost and experimental caveats. This is sufficient for an agent to understand what to expect, though it doesn't specify the exact response format (e.g., JSON) or any potential error conditions.

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?

The input schema already provides a clear description for the single 'url' parameter ('Absolute https URL of the x402 resource') with an example. Schema description coverage is 100%, so the baseline is 3. The tool description reiterates that the endpoint must be public and HTTPS, which slightly reinforces the parameter's constraints but doesn't add new semantic detail beyond 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?

The description opens with a specific verb ('Inspect') and a precise resource ('one public HTTPS x402 endpoint'), then enumerates exactly what it reports: HTTP status, payment rails, WWW-Authenticate header, Bazaar discovery extension, and a health checklist. This fully distinguishes it from the other finance/filings/crypto siblings, all of which serve different data domains.

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 states what the tool does but does not explicitly say when to use it versus alternatives, nor does it mention any sibling tool for comparison. It does imply usage (for auditing an endpoint's 402 challenge) and notes that it's experimental, but there is no 'when not to use' or alternative routing. Since the tool is unique among siblings, the omission is less critical, but explicit guidance would still be an improvement.

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