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

With no annotations, the description carries the full burden. It adds real value by disclosing data provenance (own probes), the lookback windows (7 days uptime, 30 days payers), anti-gaming filtering ('farmed wallets removed'), and the billing rule for unknown URLs. It does not say whether unknown URLs error or return an empty card, nor whether results are cached or rate limited.

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?

A single dense sentence with the core purpose front-loaded, followed by the enumerated contents and the billing caveat. Every clause adds information; there is no 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 one-parameter read tool with no output schema, the description sufficiently covers what is returned by listing the metrics. Minor gaps remain around behavior on unknown or unreachable URLs, which the billing note hints at but never resolves.

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% for the single 'url' parameter, so the description must compensate. It clarifies that the URL is an x402 endpoint (a meaningful constraint beyond the bare string schema), but adds no format, scheme, or path-level guidance and nothing about the 8-2048 length bounds.

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 resource ('Trust card for one x402 endpoint URL') and enumerates exactly what the card contains: 7-day uptime from probes, latency, last success, price, and 30-day on-chain USDC payer counts. The singular 'one endpoint URL' scope implicitly separates it from the sibling discovery tool find_x402_endpoints, so an agent can tell which to pick without opening either 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?

Usage is implied rather than stated: an agent infers this is for vetting a specific known endpoint, while find_x402_endpoints is for discovery. No explicit when-to-use or when-not-to-use instruction naming the sibling. The billing note ('Not charged for unknown URLs') gives a useful cost context but is not routing guidance.

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