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

With no annotations provided, the description carries the full burden of behavioral disclosure and does so well: it states what is returned (compliance, daily charge, estimated annual cost) and adds important UK-specific context about which zones charge private cars and how Scotland handles low emission zones. It does not describe edge cases or calculation assumptions in detail, but the core behavior is transparent.

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 fluff. The primary action is front-loaded, return values are stated, and the crucial UK context is included in a compact but valuable sentence. Every sentence earns its place.

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?

The description is complete for selecting and invoking the tool: it names the zones, states the outputs, and provides important domain context that prevents misuse. Despite lacking an output schema, the return types are explicitly described, and the parameter schema covers the inputs.

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 schema already documents all parameters. The description adds contextual meaning by tying compliance and cost to the tool's purpose, but it does not specifically explain how registration_year, fuel, and days_per_year map to the results. Baseline 3 is appropriate.

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 names a specific action (check compliance and cost) on a specific resource (UK clean air zones) and explicitly names the zones covered. It clearly distinguishes itself from the sibling cost and tax tools by focusing on emissions zones rather than general running costs or tax.

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 explicitly states 'Use for any ULEZ, CAZ, clean air zone, or emissions-charge question,' giving clear when-to-use guidance. It does not mention when not to use it or name explicit alternatives, but the sibling tools are unrelated enough that this is a minor gap.

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