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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely non-obvious behavior: a 50-pair cap, the supported travel modes, the closest-pair output, and pay-per-call pricing ($0.008 USDC via x402), which is exactly the kind of context structured fields don't carry.

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?

Three dense sentences: capability and limits first, use cases second, cost last. Every clause carries information an agent needs; nothing is padding.

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 should hint at the return shape, and 'travel time and distance matrix... with the closest pair' does so adequately for a read-only query tool. The only gap is no illustration of the lat,lon/place syntax beyond a label.

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 67%, and the weakest spot is `mode`, which has no description and no enum in the schema. The description compensates by enumerating car/truck/bike/foot, and clarifies that origins/destinations accept places or lat,lon in addition to the '| separated' format the schema notes.

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?

States a precise resource (travel time and distance matrix), scope (up to 50 origin-destination pairs) and modes, which clearly sets it apart from the single-trip `route` sibling without naming it. An agent can recognize this as the batch/matrix variant, but explicit sibling differentiation is absent.

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?

Gives concrete usage contexts ('dispatching, store finders and delivery planning') so the agent knows the intended scenario. It does not state when to prefer this over `route` (single pair) or `isochrone`, so the alternative-selection guidance is incomplete.

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