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

Annotations declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, and the description adds genuinely new behavioral facts: it consumes paid prepaid credit, charges only on verified success, and requires an authenticated ck_ principal. This billing/auth disclosure is exactly the extra context annotations cannot carry.

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?

Three short, front-loaded sentences with no filler; the paid/credit constraint leads. Slightly terse on what 'validation' actually produces, but every sentence earns its place.

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 two-parameter tool with full schema coverage, an output schema, and annotations covering the safety/idempotency profile, the description supplies the missing commercial and auth context. The only real gap is a lack of explicit contrast with the free discovery siblings.

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 coverage is 100% and both parameters (raw_intake, idempotency_key) are fully documented with constraints in the schema. The description adds nothing about parameter syntax or intent, so the baseline 3 is correct.

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?

States a specific verb (validate) and resource (XKEY intake) plus the commercial nature (PAID prepaid-credit). No sibling tool in the list validates XKEY intake, so the agent can place it, though it never names an alternative to differentiate behaviorally.

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?

'Discovery is free; execution is not' and 'commits one credit only on verified success' imply prerequisites and a cost boundary, but there is no explicit when-to-use versus when-not, nor any named discovery sibling (e.g. capability.get or x402.compatibility_audit) to route the agent.

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