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

Annotations only declare readOnlyHint and openWorldHint; the description adds substantial context on top: it performs exactly one unpaid GET, never pays, produces a single sample rather than an uptime measurement, and charges $0.001 USDC per successful call with failed calls free. Cost, side-effect profile, and sampling limitation are all disclosed.

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?

One dense sentence front-loads the core action and its full output inventory, followed by a compact scope disclaimer and a pricing note. No filler, and the most decision-relevant facts (what it does, what it does not do, what it costs) come first.

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 an output schema available, the description needn't document return values, yet it still names the observable fields. Safety annotations, cost, and sampling caveats are all covered, leaving nothing an agent needs in order to call it correctly or interpret the result.

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 single `url` parameter is already documented as a public https:// endpoint address. The description adds only indirect meaning — that the URL is fetched with one unpaid GET — but nothing about format, constraints, or error conditions for the parameter. Baseline 3 applies when the schema does the work.

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 and resource — checking an x402 (HTTP 402 payment) endpoint — and enumerates exactly what is inspected: status, 402 challenge with accepts list, networks, asset, price, pay-to address format, CORS header, response time. That profile is clearly distinct from siblings like api_sla_liveness_benchmark or cors_security_misconfig_audit.

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?

The phrase 'before you pay' gives a concrete decision point for invocation, and 'Does not pay, does not verify the seller's identity or reputation, and gives one sample, not uptime' sets explicit boundaries on what this tool should not be relied on for. It does not name a specific sibling alternative, which keeps it just short of a 5.

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