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

With no annotations, the description carries the full burden. It discloses the ranking behavior (exact-name-first, then by population) and that it returns the same full records as lookup_postal_code. It does not mention rate limits, auth, or side effects, but these are absent for a search tool; the described behavior is sufficient for an agent to anticipate outputs accurately.

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 concise (about 50 words) and front-loaded with the core purpose. Every sentence adds value: the first explains what and when, the second provides ranking details, and the third gives a crucial usage tip. No wasted words.

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 tool's moderate complexity, the description fully covers how to invoke it correctly: supported inputs, required parameter, constraints (minimum length), and output type. The ranking behavior and the hint about country are useful context. With no output schema, the mention that it returns the same records as lookup_postal_code is sufficient.

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 documents all parameters with descriptions, achieving 100% coverage. The description adds semantics for `query` by clarifying that it can be a partial postal code, and for `country` by stressing its importance. However, this adds marginal value over the schema, so a baseline 3 is appropriate.

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 the tool's purpose: finding localities by name, city, or postal-code prefix. It names specific inputs (place name, city, postal code) and outputs (postal codes), distinguishing it from siblings like lookup_postal_code by its focus on searching by name or prefix. This makes it easy for an agent to understand what the tool does.

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 provides explicit guidance on when to use the tool: when a user gives a place name and wants postal codes, or has a partial code. It also gives a clear directive to restrict with `country` when known, explaining why (names repeat across countries). This covers both when to use and how to use effectively.

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