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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true, so the safety profile is fully disclosed. The description adds behavioral details about the output (city, state, lat/lon) and the geographical coverage (60+ countries), which goes beyond the annotations.

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 only two sentences, but each sentence is information-dense and purposeful. The first sentence states the core functionality and output, the second provides usage instructions and a reference. 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 presence of an output schema (not shown but signaled), the description does not need to detail return values. It clearly explains what the tool does, the input requirements, and the extent of coverage. For a simple lookup tool with comprehensive annotations and schema, the description is complete.

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 input schema has 100% coverage with descriptions for both parameters. The description repeats this information and adds examples but does not significantly enhance meaning beyond what the schema already provides. Baseline score 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 looks up postal/ZIP codes in over 60 countries, returning city, state/region, and lat/lon coordinates. The verb 'look up' and the resource 'postal code' are specific, and the tool is well-distinguished from sibling address tools like address.ukpost.lookup or address.geocodio.geocode.

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 explicitly says to provide an ISO 2-letter country code and postal code, and mentions the underlying data source (Zippopotam.us). It does not, however, discuss when to use this tool versus regional alternatives like address.ukpost.lookup, which are present in the sibling list.

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