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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower. The description adds genuine behavioral context beyond those hints: results are distance-sorted, and demo mode imposes hard caps of 25 miles and 10 results — critical constraints an agent needs before passing larger values. It adds value without contradicting 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?

Two sentences with the core function front-loaded and the constraint sentence earning its place. Slightly cryptic phrasing ('Demo mode allows selected sample coordinates') is the only blemish; otherwise it is efficiently sized for a simple tool.

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 simple read-only tool with rich annotations, the description covers the essential behavior: input (coordinate), output (distance-sorted ZIP profiles), and operational limits (demo caps). Minor gaps remain — what fields a ZIP profile contains and whether lat/lon must be specific sample coordinates — but nothing blocks a correct call.

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 coverage is only 50% (lat/lon documented, limit and radius_miles undocumented). The description compensates by bounding the two undocumented parameters ('radius up to 25 miles, limit up to 10'), adding real semantics beyond the schema's bare defaults. It does not define exactly what a 'ZIP profile' contains, but the core meaning of each parameter is recoverable.

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 names a specific verb ('Return'), a concrete resource ('ZIP profiles'), and a distinguishing modifier ('distance-sorted ... near a coordinate'). This clearly separates it from siblings like geo_zip_lookup (lookup by ZIP) and geo_city_search (search by city), which an agent can tell apart without opening schemas.

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 context for use is implied: supply a coordinate and get nearby ZIPs. However, no explicit when-to-use/when-not-to-use guidance or named alternatives (e.g., geo_zip_lookup for reverse lookups, geo_zip_batch for multiple ZIPs) is provided, so the agent must infer routing from the description.

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