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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds real behavioral value beyond that: it flags the result as 'approximate', discloses the 5,000 km straight-line limit, and explicitly bounds the payload to distance and segments with no travel time or geometry.

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?

One tightly front-loaded sentence plus a parenthetical Korean translation; every clause earns its place (scope, limit, output bounds). The bilingual parenthetical is mildly redundant for an English-only agent but not wasteful enough to penalize heavily.

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?

With no output schema, the description usefully names the return content (distance and segments) and the approximation limit, which covers the return-value burden. However, for a 5-parameter tool at 20% schema coverage, the absence of any parameter-level guidance leaves the definition incomplete.

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 description coverage is only 20% (only 'mode' is described), so the description must compensate — yet it says nothing about the four required lat/lng inputs, their expected format, or the meaning of the mode enum values. The gap is left entirely to 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 specific verb+resource ('approximate road/land route distance between two coordinates') with an explicit scope limit (5,000 km straight-line) and output boundary (distance and segments only). It is unambiguous against siblings like gil_places_nearby or gil_hotels_nearby, though it never names an alternative to sharpen the distinction.

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?

Usage is only implied — the reader infers this is a point-to-point distance tool rather than a routing or travel-time service. The negative clause 'no travel time, no route geometry' gestures at when this tool is NOT sufficient, but no alternative tool or prerequisite is named.

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