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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond these: the 'does not assess eligibility' limitation (a behavioral constraint that prevents misuse) and the normalization behavior before another call. This is meaningful added context, though it doesn't address rate limits or data freshness.

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?

Four sentences, each earning its place: purpose, when-to-use, a behavioral caveat, and routing guidance. It is front-loaded with the key phrase 'Free coverage-discovery tool' and avoids filler. Slightly longer than minimal, but every sentence carries distinct information.

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 0-parameter tool with an output schema and complete annotations, the description covers everything an agent needs: what it returns, what it does not do, when to invoke it, and how to route to the correct sibling afterward. Nothing essential 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?

With 0 parameters, the baseline is 4. There is nothing to document, and the description correctly implies the tool takes no input and simply enumerates supported authorities. Schema coverage is trivially 100% since there are no params.

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 and resource: it's a 'coverage-discovery tool' that 'returns supported authority names.' It explicitly distinguishes itself by stating what it does NOT do ('does not assess eligibility') and is clearly differentiated from siblings by naming them directly. The title 'List supported taxi PHV authorities' reinforces the purpose.

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 explicit when-to-use guidance: 'Use when the user asks which councils or licensing authorities are supported, whether a named authority is covered, or when the authority name should be normalized before another call.' It also provides routing rules to two siblings: 'After selecting one authority use taxi_licence_preflight; for two or more authorities use compare_licensing_requirements.' This is exemplary routing guidance.

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