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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety bar is low; the description still adds real value by disclosing that output varies by credential type, naming the X-Credito and X-Wallet-Token headers, and noting the balance is shared across Radar CNPJ, PontoFato and EditalMD. It stops short of describing response shape or ordering, but there is no output schema for it to duplicate.

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 sentences, each carrying distinct information: what is returned, how credentials change it, and where wallet credentials come from. The lead sentence is a little dense and the colon construction is awkward, but nothing is redundant.

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 input parameters and no output schema, the description covers the two things an agent needs: what data comes back and how authentication state changes it. The added note that the wallet credential is issued separately per portal prevents a predictable failure mode.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline for a parameterless tool applies. The credential headers mentioned are transport-level context rather than schema parameters, and the description handles them appropriately.

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 the concrete payload the tool returns — today's free allowance, the single package, the three plans, and the balance — which goes well beyond the bare title 'Lookup plans'. However, the opening framing ('The CNPJ and address lookup service') is slightly misaligned with a plans/pricing resource and doesn't explicitly distinguish it from siblings like pricing or billing.

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 through the credential-conditioned behavior: without a credential you get the free allowance and offers, with credit or an x402 wallet you additionally get the shared balance. That tells an agent what it can expect in each state, but it never states when to pick this over the pricing or billing siblings.

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