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

Annotations already mark this read-only/idempotent, and the description adds genuinely useful behavioral context: the five distinct return categories, edge cases (no market price, non-USD pegs), zero price discovery for 'pure claim' pegs, and the auth/pricing model (prepaid header, free tier, no wallet/API key). It is consistent with the readOnlyHint annotation.

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 dense but front-loaded: the core concept and distinct output states appear first, with usage context, required input, and pricing following. Every sentence adds information, though the pricing/auth sentence is somewhat promotional for a tool-description context.

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 one parameter, no nested objects, and an output schema present, the description covers everything needed to invoke correctly: input, output categories, edge cases, when to run it, and network/costing specifics. Nothing material is missing for an agent to decide and call this tool.

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%—the only parameter 'address' is already documented as a B20 stablecoin address. The description repeats that requirement and adds marginal context (calls run over x402 on Base), but introduces no meaning the schema doesn't already convey, so it lands at 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 states a specific action—comparing a B20 stablecoin's self-declared peg against actual DEX market pricing—and names the exact output states (on_peg, depeg_warning, depegged, no_market, unverifiable_fx). It clearly differentiates itself in the B20 tool family by positioning itself as 'the missing check' that the B20 standard does not perform.

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 gives a concrete trigger ('Run before settling in any B20 stablecoin') and explains the underlying problem (currency() is self-declared and unverified). It does not name specific sibling tools to use instead or explicitly exclude alternatives, but the strong use-case framing makes when-to-call clear.

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