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

With no annotations provided, the description carries the full burden of behavioral disclosure. It conveys several behavioral traits: geodesic computation on the WGS84 ellipsoid, straight-line semantics, local computation (no network call), and no quota impact. While it does not discuss edge cases like identical or antipodal coordinates, the disclosed traits go well beyond a minimal description and there is no contradiction with any annotation.

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 short sentences with zero filler. The core result (distance in metres) is front-loaded, followed by the critical driving-distance distinction and the network/quota qualifier. Every sentence earns its place, and the structure is easy for an agent to parse.

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 two-parameter tool with an output schema present, the description is complete. It covers what the tool computes, its geographic model, the distinction from route/matrix, and performance characteristics. The output schema handles the return value, so the description doesn't need to explain it. No important decision-relevant information is missing.

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%—the schema already documents `from` and `to` as start/end coordinates and fully describes the nested lat/lon fields with ranges and a WGS84 note. The description adds little parameter-level meaning beyond naming two coordinates. This aligns with the baseline 3 for high schema coverage, where the schema does the heavy lifting.

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 immediately states a specific verb and resource: 'Distance in metres between two coordinates.' It further specifies the computational model ('geodesically on the WGS84 ellipsoid') and explicitly distinguishes itself from driving distance, which also differentiates it from sibling tools like route and matrix. Even without seeing the schema, an agent knows exactly what this tool does.

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 explicit guidance on when to use this tool versus alternatives: 'NOT a driving distance — use route or matrix for travel distance and time.' It also adds a decisive performance qualifier—'Local computation: no network call, no quota'—which helps an agent choose it when avoiding network latency or quota concerns.

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