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

Goes well beyond the annotations by disclosing the payment protocol (unpaid request returns 402 with the price, payment recorded in `cobranca`), that failed/down targets are still charged, and that a probe-network failure returns 503 with no charge. This is exactly the cost-and-side-effect context an agent needs before spending money, and it is consistent with readOnlyHint=false and destructiveHint=false.

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?

Front-loads the purpose and the return data in the first sentence, then layers payment semantics. Some phrasing is awkward and redundant ('A site that is down is the answer ... and is charged: the call was made'), but nothing is wasted given the volume of behavioral information conveyed.

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 carries the burden of explaining return values, and it does: the fields checked, `ok: false` with `reason` for down sites, 402 with price for unpaid requests, and 503 for probe failure. Nothing an agent needs before invoking a paid, non-idempotent call is missing.

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 description coverage is 100%, so every parameter (url, method, keyword, timeout_ms, expect_status) is already documented in the schema, including the note that keyword forces GET. The description adds no parameter-level detail beyond that, so the baseline of 3 applies.

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 and resource plus the exact scope: one check of one URL, returning status, response time, keyword result and TLS certificate. The phrase 'with no account and no monitor' and 'the probe of the site monitors' implicitly distinguishes it from the sibling check_site, which is a monitor-based tool.

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 description makes clear this is a one-off, pay-per-call check rather than a recurring monitor, which points an agent toward check_site for ongoing monitoring. It doesn't explicitly name that alternative or state exclusions, so it stops short of full when/when-not guidance.

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