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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds valuable behavioral context beyond that: 'the address book is left untouched', 'country-specific rules', and the specific failure result 'ADDRESS_INVALID'. The only minor gap is no mention of success return values or soft-warning behavior, so it's not a full 5.

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 compact and front-loaded: first sentence states purpose and result, second sentence clarifies non-mutation and routes to the alternative. The bilingual version is not wasteful; every sentence carries meaningful guidance.

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 covers purpose, read-only behavior, and the hard-failure result, and it identifies the correct sibling for mutations. However, with 12 parameters and no output schema, it omits what a successful validation returns, how soft failures are handled, and any input-format expectations. This is adequate but has clear gaps.

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 only 8% (only 'country' is documented), and the description does not compensate. It does not explain the meaning or expected format of name, street, city, zip, houseNumber, or other parameters, nor how they relate to the validation logic beyond the generic 'address' context. This leaves the agent to infer parameter semantics from the schema alone.

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 ('validates an address using country-specific rules') and a concrete outcome ('reports hard failures as ADDRESS_INVALID'). It also explicitly distinguishes itself from address_upsert by naming it as the tool for creating or changing an address, so an agent can tell them apart immediately.

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 usage guidance: it is 'a check only' and should not be used for mutation, and it directly names the alternative tool (address_upsert) for creating or changing an address. This leaves no ambiguity about when to choose this tool over its sibling.

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