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

Annotations already declare readOnlyHint and openWorldHint, and the description adds genuinely non-obvious behavior: the response is 'Signed', and the call is paid at $0.01 USDC per call via x402 on Base or Solana. That payment requirement is critical context an agent could not infer from the annotations.

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?

Purpose is front-loaded in the first clause, followed by the return-field inventory and two short operational sentences (signing, price). The field list is dense but earns its place given there is no output schema.

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, the description usefully enumerates the returned fields and adds the payment and signing facts. The only real gap is the undocumented parameter semantics for url/host.

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 0% for both url and host, so the description must carry the burden. 'By host or URL' tells the agent either identifier works, but it does not resolve mutual exclusivity, precedence if both are supplied, or expected format (scheme, port, path).

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 ('Price history of an x402 service') and enumerates the returned data (endpoint price, first-seen date, 30-day changes, quoted prices, market median/percentile), so an agent knows exactly what it retrieves. It does not, however, distinguish itself from price-adjacent siblings like prices_benchmarks or ai_prices.

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 implies you look up a service's price history but never states when to pick this over prices_benchmarks, ai_prices, or checks_service, nor any exclusions or prerequisites. Only the input axis ('by host or URL') hints at usage.

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