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

With no annotations, the description carries the full burden and largely does so: it discloses the data's provenance (two one-way tickets observed daily), that statistics are scoped 'desde o início da observação', and that the real round-trip price only appears 'quando existe' – an important caveat. It also instructs the agent to cite page_url. Missing: currency and any note on data freshness/latency.

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?

Front-loaded with the resource and its derivation, then a usage sentence and a citation instruction. Dense but every clause contributes; slightly long single sentence, but no filler.

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 no-annotation, no-output-schema tool, the description compensates well by enumerating the return fields (total, ida, volta, mínimo, média, preço real) and the daily-observation basis. The remaining gap is sibling disambiguation from route_price_history, which matters given how similar the names are.

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 date formats, IATA codes and automatic Portuguese city-name resolution are already documented in the schema. The description's only added parameter context is the Portuguese-name acceptance and the ida/volta pairing, which largely repeats the schema. Baseline 3 applies.

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 uses a specific verb+resource framing: historical prices for a round trip on chosen dates, and it explains the mechanism ('montada com duas passagens só ida que o passagens.dev observa todo dia') plus the returned fields. It stops short of naming the near-identical sibling route_price_history, so an agent must infer the round-trip vs. one-way distinction from the text.

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 line 'Use para quanto está ida dia X e volta dia Y e se está barato' gives a concrete usage scenario, which is better than nothing. However, there is no when-not guidance and no explicit routing against route_price_history or price_calendar, which are the obvious alternatives for the same question.

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