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

Annotations already declare readOnlyHint=true and idempotentHint=true. The description adds valuable behavioral details: it never guesses when no routable road is near, returns a 'matched:false' flag, and explains that grade_pct is a forward-compatible field that stays null for now, plus elevation may be null with a warning. This goes beyond the annotation hints.

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?

Four sentences, each earning its place: the first states purpose and output fields, the second gives use cases, the third covers parameter behavior, and the fourth explains the no-result case. It is dense yet well-structured, with the most critical information front-loaded.

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?

The tool is moderately complex (5 params, output schema present). The description covers purpose, use cases, and edge cases, and the output schema handles return structure. It could have mentioned unit auto-detection or costing defaults, but those are already in the schema, so the description is complete enough.

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 100% (all params already documented). The description adds semantic depth for include_elevation (terrain-sourced) and explicitly states grade_pct is a placeholder, clarifying forward compatibility. This improves on the schema alone.

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 begins with a specific verb ('Snap') and identifies the precise resource (road network) and the rich context returned (name, class, speed limit, etc.). It clearly answers 'what road is this point on and what are its rules?', distinguishing itself from sibling tools like reverse_geocode and map_match by focusing on road rules and single-point snapping.

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 names usage contexts: 'fleet/telematics snapping, geofence edge checks, or enriching a GPS fix'. It also clarifies the failure behavior ('Returns matched:false... never a guess'), but does not explicitly name alternatives or state when not to use this tool. This is clear context without formal exclusions.

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