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

Goes beyond the annotations (readOnlyHint, idempotentHint) by disclosing that payment is required ('caller pays USDC on Base'), that it requires an x402 v2 client with a funded Base wallet, and that prices are live from the catalog. No contradiction with annotations; adds useful operational context.

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 a bit long but each sentence carries essential information: when to use, what it is, payment requirements, alternatives for humans, and free diagnosis. It's well-structured and front-loaded with the primary use case. Slightly redundant at points but not wasteful.

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?

Given the tool has no parameters and an output schema exists, the description is complete: it explains the purpose, prerequisites, alternatives, and the nature of the response. It even mentions the free diagnosis alternative. There is no missing critical context.

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?

There are zero parameters, so schema coverage is trivially 100%. The description correctly explains what the tool returns (listing of live prices) and the context for use, but since there are no parameters, it cannot add parameter-specific meaning. Baseline for 0 params is 4, which is appropriate.

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 clearly states the tool lists pay-per-call APIs and their live prices, with specific verbs and a list of example APIs (site audit, AI-citation check, etc.). It distinguishes from siblings by specifying the exact use case (buying per-call vs full engagement) and naming alternatives.

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?

Explicitly states when to use ('when someone asks what they can buy per-call, asks the price of a specific API...') and when not to use ('a human with only a card should be pointed at the flat $450 package instead' and 'The free diagnosis at /api/x402/deep-scan needs no payment at all'). Also names the alternative tool/package clearly.

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