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

Adds value beyond annotations by disclosing the monetary cost ($0.002 USDC on Base) and the output shape (primary + independent fallback). This matters because readOnlyHint=false and openWorldHint=true, so the agent knows it is a paid, externally-sourced recommendation rather than a free lookup.

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 sentences, each earning its place: purpose, mechanism/output, and price. The critical action and cost are front-loaded with zero filler.

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 6-parameter tool with no output schema, the description covers the essentials: what it returns (primary + fallback recommendation), the decision basis (recent paid performance evidence), and the fee. It stops short of describing the response structure or pagination/error behavior, which is a minor gap given the modest 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?

Schema description coverage is 100%, so every parameter (task, q, budget, intent, freshness, max_latency_ms) is already fully documented in the schema. The description adds no parameter syntax or format detail beyond that, so the baseline of 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+resource ('Choose the best x402 provider') and elaborates the mechanism: OPX uses paid performance evidence to recommend a primary provider plus an independent fallback. An agent can tell exactly what this tool produces without opening the schema.

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?

'before spending' clearly frames the usage context — call this pre-purchase to pick a provider rather than buying blind. No siblings exist, so no alternative routing is needed, but there is no explicit statement of when not to use it (e.g., after a provider is already chosen).

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