mbta_get_route_alternatives

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

No annotations are provided, so the description must carry the full burden of behavioral disclosure. It only states that the tool returns 'alternative route options' without detailing output format, authentication requirements, or behavior in edge cases (e.g., no alternatives found). This is insufficient for a tool with no annotations.

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 long, front-loaded with the core functionality. Every sentence adds value, with no redundant or vague phrases. It is concise and well-structured.

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?

Despite having 5 parameters and no output schema, the description provides minimal information. It lacks details about the output format (e.g., whether results include transit directions, timing, or stops), pagination, or error handling. A more complete description would cover these aspects, especially given the absence of an output schema.

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 input schema has 100% description coverage, with all parameters documented. The description adds the context that the tool works 'by excluding certain modes,' which aligns with the primary_route_modes parameter. However, it does not provide additional semantic meaning beyond what the schema already offers, so the baseline score of 3 is appropriate.

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's function: 'Get alternative route options by excluding certain modes of transport.' It specifies the verb (Get), the resource (route alternatives), and the mechanism (excluding modes). This distinguishes it from sibling tools like mbta_plan_trip, which plans full trips, and mbta_get_routes, which lists all routes.

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 includes a usage context: 'useful for finding backup routes when primary transit modes are disrupted.' However, it does not explicitly state when not to use this tool or compare it to alternatives. The usage is implied but lacks exclusions or references to sibling tools.

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