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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds behavioral scope by specifying the probe window ('last 20 health probes') and the derived uptime metric, but since an output schema exists the return payload is largely already documented. It adds modest context beyond structured fields, not rich disclosure.

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?

It is a single front-loaded sentence that begins with the trigger ('Use this to check whether...'), so intent is established immediately. The parenthetical enumeration of probe fields is slightly dense but each item is informative, so nothing is wasted.

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 annotations covering safety, a 100%-covered one-parameter schema, and an output schema describing returns, the description only needs to supply purpose, trigger, and data scope — all of which it does. The only mild gap is no mention of what happens when no probes exist or the id is unknown.

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?

There is a single parameter with 100% schema description coverage ('Service id exactly as returned by x402_search'), so the schema already does the heavy lifting and the baseline is 3. The description's phrase 'one endpoint from x402_search' corroborates the id's origin but adds no syntax or format detail 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?

The description names a specific verb (check) and resource (one endpoint from x402_search), and enumerates exactly what is retrieved: the record, the last 20 health probes with status code/latency/alive, and uptime. It explicitly positions itself against the sibling x402_search as the source of the id, so an agent can distinguish it without opening the schema.

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 states a clear decision context — verifying an endpoint is 'reliable enough to pay' — and points to x402_search as the origin of the id. There is no explicit when-not or alternate-tool exclusion, so it falls short of a 5, but the intended trigger is unambiguous.

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