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

Annotations already convey read-only, idempotent, open-world, and non-destructive behavior. The description adds a demo-mode constraint listing allowed ZIP codes, which is useful, but it does not describe the returned data shape or other behavioral nuances.

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 two sentences with no filler. The primary action is front-loaded, and the demo-mode constraint earns its place by specifying valid inputs.

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?

For a one-parameter read-only lookup, the basic context is adequate, but the vague 'ZIP profile' and missing output information leave an agent without a clear expectation of the response. The demo-mode phrase is also ambiguous about whether non-listed ZIPs work outside demo mode.

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 has 100% coverage for the only parameter, providing type and an example ('U.S. ZIP code, for example 30301'). The description adds example ZIP codes for demo mode but does not meaningfully extend parameter semantics beyond the schema.

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 clear action and resource: 'Look up a ZIP profile.' The singular phrasing implies a single-ZIP lookup, which helps differentiate it from sibling geo_zip_batch, though it does not explicitly name that alternative.

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?

There is no guidance on when to prefer this tool over alternatives such as geo_zip_batch or geo_enrich. The demo-mode note lists allowed example ZIP codes but does not clarify production behavior or exclusions.

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