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

Goes well beyond the annotations by naming the external data source (Apple Maps traffic prediction), which explains the openWorldHint, by spelling out the side effect of apply=true (calendar and iCal feed reflect real ride length instead of a flat hour), and by guaranteeing that existing drop-off times are never overwritten and a failed lookup is a no-op. This effectively confirms idempotentHint and destructiveHint=false with concrete semantics.

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?

Front-loads what the tool does, then the apply semantics, then the safety guarantees; every sentence carries information. It is a long single sentence plus two shorter ones, slightly wordy but not padded.

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 still tells the agent that the result is a reported estimate rather than a value to be treated as fact, and it covers the mutation semantics and failure behavior. It could say more about the estimate's return shape or precision, but for a 2-param tool this is close to 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?

Schema coverage is 100%, so the baseline is 3, but the description adds meaning the schema lacks: not just that apply saves the estimate, but the downstream consequence (calendar/iCal show true ride length vs. a flat hour) and the protective rule that a pre-existing or user-set drop-off time is left alone. segment_id semantics remain solely in the schema.

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 specific verb (estimate) plus the exact resource (drive time of a Transfer/Transport segment) and the inputs it derives from (pickup, drop-off, pickup time). An agent can distinguish it from siblings like segment_update or get_routes without opening the schema.

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?

Clearly explains the two operating modes: apply=false reports only, apply=true persists the estimate. It also states the guardrails for when not to expect a change (existing drop-off, failed lookup). It doesn't explicitly name an alternative tool for recomputing or clearing an estimate, so it stops short of 5.

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