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

Annotations include readOnlyHint=true, which already signals a non-mutating operation. The description adds useful context: the tool mirrors the same constants the x402 gates are built from, and the live response header remains authoritative. This clarifies the data source and its relationship to the live 402 response, which is beyond the annotation. However, it doesn't disclose details like error behavior for invalid paths, or whether terms may change over time.

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?

Two sentences, dense with information: the first defines the output, the second sets expectations about authority. No filler, key details front-loaded.

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 simple one-parameter read-only tool, the description is nearly complete. It explains what the tool returns, the scope (one payable URL or product path), and the relationship to the authoritative header. Missing minor context: there's no output schema, so return-format specifics beyond the field list are absent, and there's no mention of error cases or prerequisites. But given the low complexity, the description covers what an agent needs.

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 description coverage is 100% — the only parameter, product, is described with several concrete examples. The description adds that the parameter should be a payable URL or product path, which reinforces the parameter semantics but doesn't add a lot beyond the schema's examples. Baseline of 3 is appropriate because the schema already covers the parameter well.

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 name and title already convey the resource, but the description sharpens it: 'Exact x402 payment terms for one payable URL or product path (price, asset, network, payTo, scheme).' This gives a specific verb (get/exact) and a concrete resource (payment terms for a product path), and enumerates the fields returned. It doesn't explicitly differentiate from siblings like how_to_pay_x402, but the emphasis on exact constants versus a guide is reasonably 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 implies the use case: retrieving the exact payment terms for a payable URL. It also gives a valuable usage steer: 'The live 402 response's PAYMENT-REQUIRED header remains the authoritative terms document; this tool mirrors the same constants the gates are built from.' This tells the agent when the tool is authoritative and when to prefer the live header. It doesn't explicitly say when to use check_10q_coverage or list_research instead, but the scoping to a single product path is clear.

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