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

No annotations exist, so the description carries full burden. It discloses that the call is free, requires no wallet/payment/auth, is a non-destructive probe, and mentions that paid-tier fields are null on the free tier. This covers key behavioral traits, though it doesn't mention rate limits or error handling.

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 front-loaded with the key idea ('One free call before your agent pays') and then systematically lists the verdict contents. It's slightly verbose but every sentence adds value, and the structure is logical.

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?

The tool has an output schema, so return format is covered. The description additionally explains the output fields, mentions free-tier null fields, and covers the use case. It lacks explicit mentions of error cases or rate limits, but given the simplicity (single param) it's sufficiently complete.

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%, but the description adds context: it specifies the URL must be 'absolute https URL of the x402 or MPP payment endpoint to check', which clarifies the expected format and purpose beyond the generic schema description.

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 ('probes') and resource ('URL') and clarifies that it's a trust check before payment. The description explains exactly what it returns (trust-preview.v1 verdict) and distinguishes it as a preflight, which is clear and unambiguous.

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 context for when to use it ('One free call before your agent pays') and what it does (probes without wallet/payment/auth). No siblings exist, so alternatives aren't needed, but it clearly frames the usage scenario.

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