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

Annotations already cover the safety profile (readOnly, idempotent, closed-world), so the bar is lower. The description adds real behavioral context beyond them: results are filtered to high/medium confidence links only, meaning the agent should expect partial or empty coverage rather than exhaustive matches.

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?

Three short sentences with the resource named first, then the input formats, then the confidence filter, then the use case — well front-loaded. The input-format parenthetical is mildly redundant with the schema, a minor waste.

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 lookup with annotations and no output schema, the definition covers scope (IT companies only), input flexibility, confidence filtering, and the intended outcome (CNPJ discovery). Only the relationship to the CNPJ-based sibling is left unaddressed.

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 parameter already documents 'Domínio, URL ou e-mail, ex.: linx.com.br'. The description's parenthetical repeats that accepted-format fact rather than extending it (no normalization rules, no subdomain behavior), so baseline 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 specific verb+resource: Brazilian IT companies tied to a domain, accepting URL or email. The scope restriction ('Empresas de TI') and the stated goal of discovering a CNPJ make the direction of the lookup clear, implicitly the inverse of the sibling empresa_por_cnpj, though the sibling is never named.

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?

'Útil para descobrir o CNPJ de um site' gives a concrete use case, which is more than nothing. However, it never says when to prefer the sibling empresa_por_cnpj (the CNPJ→company direction) over this domain→CNPJ direction, so routing is left to inference.

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