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

There are no annotations, so the description carries the behavioral burden. It discloses the calculation approach (cost per km, real fuel efficiency), the output value (monthly savings in reais), and the extra nuance of the 70% rule and when it fails. It does not deeply discuss edge cases, but the core behavior is clearly described.

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 with no filler: the first states the main purpose and method, the second adds the key secondary output, and the third lists the parameter contract. Everything is front-loaded and necessary.

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 output schema and no annotations, the description satisfactorily covers what the tool computes, what it returns conceptually, and which parameters are required vs. optional. It could mention default yield assumptions, but the schema already covers those defaults, so nothing critical is missing.

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 coverage is 100%, so the baseline is 3. The description adds value by explicitly separating required from optional parameters and warning to use the exact English parameter names—useful given the Portuguese-language description. This goes just beyond restating the 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 states a specific verb ('Compara') and a specific resource (álcool e gasolina), plus the exact comparison basis (custo por quilômetro rodado). This clearly distinguishes it from sibling tools like compare_investments or compare_loans without needing to open the schema.

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 description gives clear context for when to use the tool: whenever comparing alcohol vs. gasoline by cost per km using real car performance. It does not explicitly name alternatives or state when not to use it, but the subject matter is narrow and unambiguous enough to route an agent correctly.

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