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

Annotations already cover the safety profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false), and the description adds real context beyond them: omitted settings inherit account defaults, the call returns a route_id, and the underlying endpoint is POST /ext-create-route. The non-idempotency warning reinforces rather than contradicts the annotation, and nothing here conflicts with destructiveHint=false.

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?

A single dense paragraph with the WRITE marker front-loaded, the field inventory next, then defaults, return value, sibling handoff, and endpoint. Every clause carries distinct information and none repeats the schema verbatim.

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?

Although there is no output schema, the description states the return value (route_id), explains defaulting behavior for the six all-optional parameters, and points to the sibling needed to make the route useful. Nothing an agent needs before calling 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 coverage is 100%, so baseline would be 3, but the description adds meaning the schema cannot: any omitted setting falls back to the account's defaults, which explains why all six parameters are optional. The parenthetical field list also gives a quick orientation across the six settings.

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?

Opens with an explicit verb+resource ('WRITE: create a new, empty route') and enumerates the configurable settings in parentheses. It also contrasts itself with siblings by directing follow-up work to upper_create_stop, so the agent can distinguish it from upper_update_route without opening either 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?

Clear about the creation context and explicitly names the alternative path for adding stops ('add stops with upper_create_stop'), plus warns that calling it twice creates two routes. It does not spell out when to reach for upper_update_route instead, but the create/update split is self-evident from the name.

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