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

Annotations already declare safe, read-only, idempotent behavior. The description adds the ordering (closest first) and that distance in miles is returned. However, it omits the limit parameter behavior (default 25, max 50), implying 'Every US ZIP' even though results are capped. This is a meaningful behavioral gap for an agent to know.

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 a single, front-loaded sentence that conveys the core operation and key output detail. There is no verbosity or redundancy; every phrase contributes to understanding.

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 tool with five parameters and no output schema, the description is reasonably informative but incomplete. It lacks information about the result cap (limit), does not specify that a center point is effectively required despite schema allowing only miles, and does not describe any pagination or additional output fields beyond distance. An agent would need to infer or experiment to fully use it.

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?

With 0% schema description coverage, the description must compensate. It explains 'miles' as the radius and that the center can be a ZIP or lat/lon. However, it does not explain the 'limit' parameter or clarify that either zip or lat/lon should be provided (only miles is required in schema). It partially covers the parameter semantics but misses key details.

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 function: return every US ZIP within N miles of a center point (ZIP or lat/lon), sorted closest first, with distance included. It is specific about the resource and behavior, and the phrase 'Every US ZIP' distinguishes it from siblings like nearest_zip (returns a single one) and zip_distance (calculates distance between two given points).

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 no explicit guidance on when to choose this tool versus siblings such as nearest_zip or zip_lookup. It does not mention scenarios, exclusions, or alternatives. The purpose is clear, but the usage context is left entirely to inference.

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