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

Annotations already provide readOnlyHint and idempotentHint, so the tool's safety profile is clear. The description adds that the output is base64-encoded and lists event types, but does not disclose additional traits like size limits or error responses. No contradiction with annotations.

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 with no superfluous words. Clearly states action, input, and output. Efficiently front-loaded.

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 download tool with no output schema, the description covers the return format (base64) and event types. It lacks details on error handling or constraints but is adequate for the complexity. No missing critical information.

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?

All three parameters are fully described in the schema (100% coverage), so the description adds minimal value. It loosely maps 'chave de acesso + número sequencial' to ChaveNF and NuProtocolo, but this is already implied. No new semantic depth beyond schema.

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 tool downloads event files (CC-e, cancellation, etc.) by access key and sequential number, returning base64. However, it uses 'número sequencial' while schema calls it 'NuProtocolo' (protocol number), causing slight ambiguity. The name and description sufficiently distinguish from siblings like 'arquivo_baixar' and 'arquivo_baixar_periodo'.

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?

No explicit guidance on when to use this tool versus alternatives (e.g., 'arquivo_baixar' for general files). The description implies it's for event-specific downloads but doesn't state exclusions or provide comparative context.

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