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

With no annotations, the description carries the full burden and does well: it states the tool is free and read-only, that it makes no payment, and explicitly bounds its claim ('does not certify functional correctness'). It still omits failure behavior when no service matches and any rate/caching characteristics.

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 tight sentences with the core purpose and the no-payment guarantee front-loaded; every clause carries information and nothing is padded.

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 no output schema and no annotations, the description does sketch the return contents (mapped stable-asset price plus public usage evidence) and disclaims correctness. However, it leaves mode semantics, price-filter behavior, and the no-match case unexplained for a 3-parameter selection 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 description coverage is 0%, so the description must compensate, and it does not: it never explains mode values (CHEAPEST/BALANCED/PROVEN/STRICT) or how max_price_usdc constrains selection. Only the enum labels themselves hint at meaning, leaving the key behavioral parameter undocumented.

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 verb+resource: a 'selector for supported x402 services,' and clarifies it returns price and usage evidence rather than executing anything. It is clear what the tool does, but it never contrasts itself with the siblings market_capabilities or omega_evidence, so the agent must infer the routing role from the name alone.

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?

There is no explicit when-to-use or when-not-to-use guidance and no mention of the sibling alternatives. 'Makes no payment' hints that this is a pre-payment discovery step, but that is inference rather than stated guidance, and nothing tells the agent how the four modes affect selection.

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