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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds value by disclosing the cost aspect ('Free') and the specific output dimensions (resolvability, coverage, confidence, price), which are not present in annotations. This extra context goes beyond the structured safety hints.

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?

The description is a single 12-word sentence, front-loaded with the key differentiator 'Free', and contains zero redundant words. Every word earns its place.

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 simple one-parameter tool with robust annotations, the description adequately covers the purpose and expected output dimensions. It lacks a detailed output format, but no output schema exists and the estimate is conceptually clear, making the description sufficient for this complexity level.

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?

The input schema fully describes the only parameter ('cnpj' as a Brazilian CNPJ, 14 digits) with 100% coverage. The description simply uses the same term without adding new syntax or format details, so the baseline of 3 is appropriate.

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 clearly states the verb ('estimate'), the resource ('CNPJ'), and the scope ('resolvability, coverage, confidence and price') with a temporal context ('before paying'). It differentiates from sibling tools like 'quote' by emphasizing 'Free' and the pre-payment nature, making the tool's unique role explicit.

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 context 'before paying' clearly indicates when to use this tool, and 'Free' suggests an economical pre-check. However, it does not explicitly mention alternatives or exclusions, so the guidance is clear but not exhaustive.

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