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

Annotations cover the safety profile (readOnly, non-destructive, idempotent), and the description adds high-value behavioral facts beyond them: optional 402-probing, a free sample vs paid full result, the exact price ($0.025 Base USDC via x402), and that discovery is unvetted/raw. This is exactly the kind of economic and freshness context annotations cannot convey.

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?

Front-loaded purpose sentence, then usage, then constraint, then economic model. Dense but every clause carries routing or pricing information. Slightly cluttered by the mixed parentheticals but nothing is wasted.

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 paid discovery tool with an output schema present, the description covers what an agent needs: what it returns, when to use it, cost, and the free-sample/paid split. Minor gap: it doesn't state whether the 402-probe is default-on or requires a flag.

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 baseline is 3. The description adds the intent of the query param ('optional count n 10-80') and the payment/probing behavior surrounding it, though it leaves some ambiguity about how 'query' maps to free sample vs paid call. Slightly above 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?

States a specific verb+resource ('Return a fresh timestamped list of live x402 endpoints') with explicit data sources (PayAI, CDP) and names the sibling it excludes (phantom-allowlist). An agent can distinguish this from all other discovery tools 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?

Explicit when-to-use ('when you need discovery leads of payable agent APIs') and an exclusion with a named alternative ('Not for vetted payable sellers only — use phantom-allowlist'). This is textbook routing.

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