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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: data provenance (Receita Federal), the full field surface returned, and the accepted input formats including alphanumeric CNPJs. It omits error/not-found behavior and any rate-limit or caching traits.

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?

Two sentences: the first front-loads the source and then enumerates returned fields (valuable since there is no output schema), the second covers input formats. The long field list earns its place because it substitutes for a missing return schema.

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 field enumeration makes the description largely self-sufficient, and the input-format sentence closes the main calling ambiguity. What remains uncovered is edge-case behavior — what happens for inactive, invalid, or not-found CNPJs — which matters for a single-param lookup but is secondary.

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%, so the baseline is 3, but the description genuinely adds meaning the schema lacks — the schema example only shows numeric formats ('11.222.333/0001-81' or '11222333000181'), while the description states that alphanumeric CNPJs are also accepted, with or without punctuation.

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 concrete lookup resource (public data of a Brazilian company from Receita Federal) and enumerates exactly what comes back — legal name, CNAE, address, partners, debt/sanction flags. An agent knows precisely what this tool retrieves 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?

Usage is implied: it is a CNPJ-keyed company lookup, and the phrase 'empresa brasileira ativa' hints at active-company scope. But there is no explicit when-to-use guidance, no statement about behavior for inactive or nonexistent CNPJs, and no alternatives to route to (none exist among siblings).

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