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

Annotations already establish read-only, idempotent, and non-destructive behavior. The description adds the useful behavioral nuance that the surface is 'live' and 'canonical,' implying fresh, authoritative data. No contradiction; it just omits deeper details that are unnecessary for this simple read operation.

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?

A single sentence with no filler. The verb and resource are front-loaded, and the usage condition is appended economically at the end.

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 zero-parameter, read-only readiness check with rich annotations, the description covers what the tool does, when to use it, and the nature of the operation. No output schema exists, but none is needed at this level of complexity.

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 has zero parameters and full schema description coverage, so the baseline is 4. The description correctly implies there is no input to configure, and no additional parameter meaning is needed.

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 names a specific resource ('live canonical payment-rail readiness surface') with a concrete verb ('Read'), and the phrase 'before attempting a paid call' frames it as a pre-call gate. This clearly differentiates it from sibling tools like call_capability, x402_contract, and system_status.

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 explicitly states when to use the tool: before attempting a paid call. It does not mention when not to use it or name alternative tools, so it lacks the explicit exclusions needed for a 5, but the usage context is clear and actionable.

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