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

Annotations already declare read-only and idempotent behavior. The description adds meaningful context: it computes by road, and can handle future departure or arrival-time queries. It doesn't mention response format or potential limitations, but the existing annotations cover safety, so the bar is met.

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 sentences, front-loaded with the core purpose, and concise. It avoids redundancy with schema details and earns every word.

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 has 9 parameters, no output schema, but good annotations. The description explains the core function and two common modes (depart at, arrive by), which are key for usage. Without an output schema, it implies the result is a duration, which is sufficient. Slight gaps like coordinate usage are covered in the schema, so overall it's complete.

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?

Input schema covers all 9 parameters with descriptions (100% coverage). The main description adds general context ('by road', time-based queries) but doesn't provide additional per-parameter meaning beyond the schema. Baseline 3 is appropriate given the schema already 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 clearly states the tool calculates travel time between two places by road, distinguishing it from straight-line ('as the crow flies') distance. It also notes time-based queries (future departure or arrive-by), making the purpose specific. It doesn't explicitly differentiate from sibling tools like routes_directions, but provides enough context.

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 some usage context—when to ask about future departure or arrive-by times—but does not explicitly state when to use this tool over alternatives. It implies it's for travel time rather than directions, but lacks direct exclusions or alternative tool names, leaving the agent to infer.

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