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

Adds real context beyond the read-only/idempotent annotations: it is free, subject to normal rate limits, and it defines the 'blocked' handshake state (URL/redirect/DNS not allowed by policy) rather than leaving the enum opaque. It also discloses the freshness fields (age, stale flag) so the agent knows results may be cached. It stops short of saying how the probe is triggered or how long results persist.

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?

Leads with 'FREE.' and then the question the tool answers, so the key affordance is front-loaded. The second half is a dense run-on list of return fields, but every clause carries information.

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-only lookup with no output schema, the description covers what is returned, what the status values mean, and the cost/rate posture. Minor gaps remain around result caching behavior and what 'covered' formally means.

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% and the url parameter already carries an example, so the schema does the heavy lifting. The description implies that a bare hostname is acceptable (as in 'seller hostname or URL') but adds no format or resolution rules beyond what the schema states.

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 query — coverage status plus latest probe result for an x402 seller or remote MCP server — and enumerates the returned fields (handshake state, protocol version, tool count, tools hash). It is clear on its own, but never distinguishes itself from sibling tools like 'check' or 'coverage', which sound like overlapping lookups.

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?

'Use before paying any x402 seller' gives an explicit precondition for invocation. There is no statement about when not to use it or which sibling to pick instead, so the guidance is clear but not complete.

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