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

With no annotations, the description carries the full behavioral burden. It usefully discloses input flexibility (punctuation optional, 8-digit root resolves to the matriz) and enumerates the returned data blocks, but says nothing about not-found/error behavior, permissions, or rate limits.

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?

A single dense sentence that front-loads the selector (CNPJ and its accepted forms) before listing return contents. Every clause carries information, though the trailing enumeration of data domains is long and could be trimmed.

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?

There is no output schema, so the description's enumeration of returned fields (registration, Simples/MEI, address, CNAEs, partners, establishment count) is genuinely necessary and present. The only gap for a one-parameter read tool is the absence of error/not-found semantics and sibling routing.

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 0% and the single parameter is completely undocumented in the schema, so the description must compensate. It does so well, specifying the 14-digit CNPJ format, punctuation tolerance, and the 8-digit root shortcut that changes the result to the matriz.

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 resource (one company) retrieved by a specific identifier (CNPJ) and enumerates the data domains returned, which lets an agent distinguish a single-record lookup from bulk siblings like search_companies or count_companies. It stops short of explicitly naming those siblings, so it is clear but not fully differentiated.

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 rather than stated: pass a 14-digit CNPJ for a company or an 8-digit root to get the matriz. There is no explicit when-to-use/when-not guidance and no routing to alternatives such as search_companies when the exact CNPJ is unknown.

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