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

Beyond the read-only/idempotent annotations, the description discloses the return shape (normalised single-line form and named issues), the limitation that it is not proof of deliverability, supported country scope, and access/pricing behavior including the x-credit-token header and free daily tier. This gives the agent meaningful behavioral and operational context.

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 front-loaded with the core purpose and delivers useful operational details in a compact set of sentences. Minor redundancy exists between 'TR/US/EU' and the later country list, and the pricing sentence is slightly dense, but nothing is wasted overall.

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?

Given the output schema, annotations, and parameter schema, the description covers the tool's purpose, inputs, output behavior, limitations, and access requirements well. It does not describe fallback behavior for unsupported countries or explicitly route to sibling tools, but those gaps are minor for this tool's scope.

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 has 100% description coverage for all five parameters, so the baseline is 3. The description reinforces that country, line1, and city are required and mentions postal patterns, but it does not add significant new meaning beyond the schema's own parameter descriptions.

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 clearly states a specific action: a structural address check for postal patterns across common countries, with a normalized output and named issues. It also distinguishes itself by explicitly saying 'Not proof of deliverability,' which separates it from deeper address intelligence or verification siblings.

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?

It gives a clear usage context ('before you ship') and an explicit exclusion ('Not proof of deliverability'). However, it does not name any alternative tool for cases where deliverability proof is needed, so the guidance is strong but not fully complete.

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