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

Annotations already declare readOnlyHint and openWorldHint, and the description adds genuinely new context: no payment is required and each rule returns one of four discrete verdicts. It stops short of describing auth/rate-limit behavior or what a response envelope looks like.

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?

Three sentences, front-loaded with the 'Free' differentiator and the core action; the verdict vocabulary follows naturally. Minor cost: the accept_proof sentence carries a slightly dense embedded example.

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?

No output schema exists, so the description takes on return-value disclosure and does explain the four verdict states per rule. Adequate for a 2-parameter read-only tool, though the overall response shape beyond the per-rule verdicts is not described.

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, but the description meaningfully upgrades the notably vague schema text for accept_proof ('Optional Accept-Proof value') by supplying a concrete syntax example ('sample=attested; price<=listing') and stating what the parameter answers.

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 concrete verb+resource ('check any x402 offer's Fair Offer block') plus scope qualifiers ('from outside, without paying'), which cleanly separates it from siblings like lint_listing or signed_sample that operate on listings or samples rather than an external offer.

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?

It gives one concrete usage cue — pass accept_proof to check an offer against buyer requirements — but never states when to prefer this tool over lint_listing or the other validation-adjacent siblings, leaving comparison to inference.

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