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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=true. The description adds genuinely useful behavior beyond that: no financial obligation is created, the quote_id is opaque, a TTL applies, and settlement requires an EIP-3009 signed voucher. It does not state what happens when the TTL expires, which keeps it from a 5.

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 tight sentences, front-loaded with what it returns, then the zero-cost guarantee, then the settlement flow. No filler and the most decision-relevant facts come first.

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?

With an output schema present, the description is not obligated to enumerate return fields, yet it still names the key ones. Combined with the settlement flow and zero-cost caveat, an agent has enough to call it correctly; only TTL/expiry behavior is left implicit.

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%, so 'tool' and 'amount' are already documented in the schema (including the example and default). The description adds no further meaning about parameter values or formats, so the baseline 3 applies.

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 and resource ('returns the live price, an opaque quote_id, TTL, and the settlement URL') and frames the tool's role as the zero-cost pricing hook preceding code402 tool calls. This clearly separates it from the sibling validation tools (iban_check, gstin_check, etc.), none of which produce quotes.

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?

Explains the usage context well: call it first to feed pricing into a planner's context, then hit settlement_url only if acting on the quote. It gives the when and the conditional follow-up but stops short of naming an explicit alternative tool or a when-not-to-call exclusion.

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