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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, openWorld), but the description adds information none of them carry: $0.002 per call via x402 on Base, the prepaid x-credit-token header for unlimited calls, 1 free call/day per tool, and no API key required. That is exactly the auth/cost/rate-limit context an agent needs before invoking a metered tool.

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?

Front-loaded with the core purpose and the key exclusion before pricing details, and every clause carries information. The dash-separated phrasing is dense and slightly repetitive ('Structural address check: country, street, city' restates the opening), but it stays compact 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?

An output schema exists, so return values need not be explained, and the description still sketches them lightly ('normalised single-line form and named issues'). Cost, auth and the deliverability caveat make it largely self-sufficient; the country coverage stays vague ('common countries', '…') without saying what happens for unsupported countries, which is the one remaining gap.

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 description coverage is 100% for all five parameters, so the schema already documents country (ISO-2), line1/line2, city and postal. The description restates the required set (country, line1, city) and the covered country set, but adds no format or syntax detail beyond the schema. Baseline 3 applies.

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?

States a specific verb and resource: a structural postal/address format check covering country, street, city and postal patterns, naming the covered regions (TR, US, GB, DE, FR, NL). It also explicitly draws the boundary that separates it from validation-type siblings by saying it is 'Not proof of deliverability', so an agent can place it against address_intel, address_trust and address_label.

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?

Gives a clear usage moment ('before you ship') and an explicit exclusion ('Not proof of deliverability'), which prevents the common misread of this as a deliverability validator. It does not name a specific sibling alternative, so it stops short of full when-to-use/when-not routing.

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