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

With no annotations, the description carries the full burden. It discloses detection methods (threat feeds, heuristics, reputation graph), the output format, and the free vs. paid distinction (free lacks signed attestation). It does not cover error handling or data retention, but the core behavior is well explained.

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 three sentences, each serving a distinct purpose: purpose, usage guidance, and free/paid alternative. It is front-loaded with the main action and contains no fluff.

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 simple tool with one parameter and no output schema, the description fully covers what it returns (score and risk band), the threat detection logic, and the appropriate usage context. It also mentions the paid alternative for richer output, making it complete for an agent to decide when to use it.

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?

The schema already provides 100% coverage for the single 'target' parameter with the description 'Counterparty URL or hostname.' The description repeats this but adds no new semantics, so the baseline score of 3 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's primary function ('Check whether a counterparty is SAFE TO PAY'), specifies the input (URL or host), and describes the output (0-100 trust score and risk band). It also distinguishes this free lightweight check from the paid endpoint that provides full reasoning and attestation.

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?

Provides explicit when-to-use guidance: 'Call this before paying any merchant, API, agent, or x402 resource.' It also gives a clear alternative for when more detail is needed (paid POST /v1/check endpoint), which effectively tells users when not to use this tool.

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