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

The description goes well beyond the annotations by disclosing the payment mechanics: an unpaid request returns 402 with the price, a paid request returns the check plus the charge in `cobranca`, and an unavailable check returns 503 with nothing charged. It also guarantees the check never visits the target address, which is important side-effect information for a paid, non-read-only call.

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?

Five sentences, front-loaded with the purpose and then payment and failure behavior, with no filler. It is slightly denser than needed, but each sentence carries operational 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 paid, non-idempotent call with no output schema and sparse annotations, the description covers the crucial missing pieces: cost flow, 402/503 behavior, and the no-visit guarantee. It is thin on the exact shape of the returned check ('what we measured, the catalog listings and the domain facts' is not elaborated), which is a minor gap given no output schema exists.

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 one parameter with 100% schema description coverage, so the schema already defines it as the http(s) endpoint without credentials. The description adds only a marginal nuance – that the check never visits the address – without elaborating on format or constraints beyond the schema, matching the baseline 3 for fully documented params.

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 states a specific verb and resource – it checks an MCP server address and returns what was measured, catalog listings and domain facts, and identifies itself as the answer of `GET /api/check`. It is clear what the tool does, but it never distinguishes itself from close siblings such as `check_tool` or `listing_status`, leaving the agent to infer which check to call.

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 gives clear context for when this tool applies: 'sold per call to agents, with no account and no allowance before', implying use when no account or allowance exists. It does not name alternatives or state when-not to use it, so it falls 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.