Straight-line distance

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

Annotations already declare readOnlyHint=true, so the description does not need to re-emphasize safety. The description adds value by noting the tool is 'instant' (performance characteristic) and 'independent of road network' (limitation). This provides helpful behavioral context beyond the 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 exceptionally concise: two sentences, no wasted words. It front-loads the core concept ('Great-circle distance') and immediately provides usage differentiation. Every sentence earns its place.

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 simple (two required string parameters, no nested objects, no output schema). The description covers the mathematical concept, performance, and when to use alternatives. While it doesn't specify the return format (e.g., units), the overall context is sufficient for an agent to correctly select and invoke the tool.

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%, with each parameter having a clear description (place name, address, or coordinates). The tool description does not add any additional meaning to the parameters beyond what the schema already provides. Baseline of 3 is appropriate.

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 defines the tool's purpose: calculating great-circle ('as the crow flies') distance between two places. It uses a specific verb phrase ('distance between') and distinguishes itself from the sibling route tool by explicitly stating this is not for road distances.

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 provides explicit guidance on when to use this tool ('instant and independent of any road network') and when not to, with a direct alternative ('use route for real travel distances'). This is exemplary usage direction.

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