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

Annotations already declare readOnly/idempotent/non-destructive behavior, so the bar is lower. The description adds valuable context: the data source (Autoridade Tributária), quality assurance across all 308 municipalities, and the important behavior of explaining per-parish rates instead of returning zero.

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 the core purpose first, followed by data provenance and a key edge-case caveat. Every sentence adds distinct value and there is 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 single-parameter lookup whose safety profile is fully covered by annotations, the description is nearly complete. It explains accepted inputs and the main exception, though the absence of an output schema means the exact response format is slightly under-specified.

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 schema already describes the single parameter at 100% coverage, so the baseline is 3. The description adds concrete accepted formats and examples (Portuguese name or four-digit code), which meaningfully clarifies how to supply the municipality value.

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?

Title and description name a specific verb ('Look up') and resource ('IMI rate of a municipality'), with the input forms (name or four-digit code) made explicit. This clearly distinguishes it from the sibling cost/calculation tools.

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 makes clear what the tool does and when its edge case applies, but it never explicitly tells the agent when to prefer this over imi_annual_cost or imt_calculate. Usage is implied rather than directly guided.

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