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

Annotations already mark readOnlyHint and openWorldHint; the description adds useful behavior: it sends no payment headers, makes an external fetch, returns a risk note, and does not spend money. It does not elaborate on timeouts, non-402 responses, or rate limits, but for a read-only probe these are not critical.

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?

Most of the content is task-relevant, including the output field list and next-action pricing, so it is richer than a bare stub. However, it is a dense run-on with branding ('by AI Nock') and unexplained jargon ('x402 wash/honesty probe', 'has402') that could be tightened.

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 enumerates the returned values and the always-present next options, which an agent needs to interpret the result. It remains slightly incomplete about non-402 responses and what 'has402' means, but the one-parameter tool is otherwise well covered.

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 sole parameter url is fully documented in the schema with 100% coverage, and the description mostly restates the same 'no payment headers' constraint. It adds no new semantics about URL format or behavior beyond the schema.

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 operation — fetches an http(s) 402 URL without payment headers — and lists the returned fields, so an agent understands what check does. It does not explicitly distinguish itself from sibling check_batch or related paid actions, so it doesn't fully earn a 5.

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?

Explicitly says 'Use before paying any x402 resource,' giving a clear condition for selection. It doesn't discuss exclusions or compare with alternatives, but the single directive is sufficient for most routing decisions.

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