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

With readOnlyHint=false the description correctly signals a state-creating operation, and it goes beyond annotations by disclosing the auth requirement (edm_ token), the free-first/subsequent-paid quota model with a 30-day window, periodic check cadence, and the one-shot nature of prazo notifications. It stops short of saying how to inspect or remove a vigia (the vigia_eventos sibling is never referenced).

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 pricing statement is stated twice in near-identical form ('A primeira é grátis; as seguintes custam…' then 'A primeira vigia ativa é grátis (FRANQUIA_VIGIAS); as seguintes custam PRECO_VIGIA…'), which is pure waste. The token requirement is also embedded mid-sentence rather than front-loaded, weakening scanability.

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?

No output schema exists, and the description compensates by explaining what events are registered and how notifications behave, plus cost and auth. For a 3-param mutation it is largely complete, with only the retrieval/removal path via sibling tools 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 description coverage is 100%, so canal, destino, and compra_id are already documented in the schema, fixing the baseline at 3. The description adds only the token requirement and no additional syntax or format detail for the three parameters.

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?

Clear specific verb+resource: 'Vigia uma compra', and it enumerates exactly what it watches for (retificação, documento novo, suspensão, prazo adiado, valor, avisos de prazo). It does not, however, contrast itself with plausible siblings like criar_alerta, alertas_compras, or vigia_eventos, so an agent isn't told which monitoring tool to pick.

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?

It states a precondition ('precisa do token edm_…') and cost/quota behavior, which is genuine usage context, but there is no explicit when-to-use vs. when-not or any routing to the alert-related siblings. Usage is implied rather than directed.

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