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

Annotations only declare readOnlyHint=true. The description goes well beyond that: it explains the exact number of entries (eleven), the naming conventions (crossingName as route code, readable name in location.description), the lane structure for each crossing, and the behavior when no data is available (waitTimeInMinutes omitted). This provides rich behavioral context that an agent needs to interpret results correctly.

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 clear and efficient. It front-loads the core purpose, then provides specific structural details (lane counts, naming scheme, data omission behavior) without redundancy. Each sentence adds new information, and the structure flows logically from overview to specifics.

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?

Given the tool has no parameters, is read-only, and has an output schema, the description covers everything needed: the specific crossings, lane variations, naming conventions, and missing-data behavior. Even though the output schema exists, the description explains the semantics of the fields, making the tool self-contained and easy to invoke without external context.

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?

The tool has zero parameters, so the description correctly avoids mentioning any. The baseline for 0 params is 4, and the description doesn't need to add parameter semantics. It does provide context about the output structure, which is more relevant than parameter details here.

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 uses a specific verb ('Returns current vehicle wait times') and a clear resource ('WA→Canada land border crossings'). It lists the exact border crossings and lane types, distinguishing it from sibling tools like ferry alerts, mountain passes, or toll rates. The scope is unambiguous.

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 final sentence explicitly states when to use the tool: 'Use for "how long is the border wait?" questions.' It also clarifies that crossings without current data are still returned, which sets expectations. It doesn't explicitly say when not to use it, but the sibling tools are clearly distinct domains (ferries, passes, tolls), so exclusions are implicitly obvious.

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