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

The readOnlyHint annotation already flags this as a read operation, so the description doesn't need to repeat that. It adds meaningful context by explaining the relationship between route IDs and alert route IDs, including the caveat about excluded alerts. This goes beyond the structured annotation and helps the agent interpret results correctly, though it omits details like refresh timing or sort order.

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 sentences, each earning its place: the first states the core function, the second explains the correspondence and exceptions, and the third points to the alternative. The main purpose is front-loaded, and there is no redundant or filler content.

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's simplicity (one optional parameter, read-only, output schema provided), the description is complete. It covers the tool's purpose, its relationship to alerts, and the alternative for terminals. No missing information would prevent an agent from calling it correctly.

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 schema describes the tripDate parameter completely (ISO 8601 format, optional, defaults to today), achieving 100% coverage. The description does not add further parameter-specific detail, which is acceptable given the schema already handles it. The baseline of 3 applies because the schema carries the full parameter meaning.

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 'Returns the main WSF ferry routes operating on a given date.' This specifies the verb, resource, and temporal scope. It also distinguishes itself from siblings by explicitly mentioning the correspondence to impactedRouteIds in ferry alerts and naming the alternative for terminal IDs, so an agent can differentiate it without opening schemas.

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 explicit guidance: it tells when to use this tool (to get routes for a date) and when it may be insufficient (some alert route IDs like seasonal, San Juan interisland, or Sidney B.C. may not appear). It also directs the agent to wsdot_get_ferry_terminals for terminal IDs, leaving no ambiguity about the appropriate tool choice.

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