Validate a postal-code policy

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

The annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavior beyond annotations: it states that only post_code is inspected, and that unknown country or missing post_code returns non-compliant with a descriptive error rather than raising. This is exactly the kind of extra behavioral context that helps an agent.

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?

The description is well-structured: a one-sentence summary, a compact list of supported policies, a scope note, and a clear Args/Returns breakdown. Every sentence contributes operational knowledge and the most important information is front-loaded.

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 validation tool with two required parameters, full schema descriptions, rich annotations, and an explicit return format, the description covers all essential operational details: supported formats, input shape, return keys, and error behavior. There is no significant missing information an agent would need to invoke it correctly.

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 has 100% parameter description coverage, so the baseline is 3. The description adds meaningful value by enumerating the exact country code formats (e.g., US 5-digit ZIP or ZIP+4, GB alphanumeric) and emphasizing that only the post_code field of the address is considered. This supplements the schema descriptions usefully.

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 opens with a specific verb-resource pair: 'Validate an address's post_code against a country's format policy.' It also clarifies the exact scope (only post_code is inspected) and lists the supported country policies, making the tool's role distinct from siblings like assess_address or remediate_address.

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 clearly states the supported policies (US, GB, DE, FR, JP) and the condition of the tool—it only inspects post_code, not other address fields. It gives adequate context for when to use it, but it does not explicitly mention alternatives or state when not to use it relative to sibling tools.

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