Verify an x402 endpoint

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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces this by stating 'Check' – a read-only operation. It adds valuable behavioral context: 'Paid (x402) unless an evaluation key is configured,' informing the agent of potential cost implications. It also explains what data it checks (live price/payee vs catalog), which is not available from annotations alone. No contradictions.

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 sentences, front-loaded with the core purpose and checks, followed by usage guidance and cost note. There is zero waste; every sentence earns its place. The structure is efficient and immediately scannable.

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?

For a single-parameter tool with no output schema, the description conveys the purpose, when to use it, and the key behavioral trait (payment). It implies what the tool returns (whether it is live, matches, and timestamps of changes), but does not explicitly state the response format. Since the tool is straightforward and the description is otherwise thorough, this minor gap is acceptable.

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 schema description for the only parameter is 100% complete, defining 'resource' as 'Absolute URL of the x402 resource to check.' The tool description adds no further parameter detail, merely echoing the same concept. Since the schema fully covers it, the description adds no semantic value beyond the baseline.

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 clearly states the verb 'Check' and the resource 'x402 endpoint', and specifies the exact checks performed: live/payable status, price/payee match with the catalog, and when changes occurred. This distinguishes it from sibling tools (retrieve_secret, store_secret) which deal with secrets, leaving no ambiguity about its role.

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?

Provides an explicit usage context: 'Use before the first payment to an endpoint you have not used.' This tells the agent when to invoke it. It does not mention when not to use it or alternative tools, but the siblings are unrelated in purpose, so no confusion arises. The payment condition also adds usage context.

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