Zipcar MCP Server

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

Without annotations, the description carries the full burden. It discloses the parking constraint and return value structure ('trip summary with duration, miles, and cost'), but fails to indicate this is a destructive/irreversible operation or describe error states.

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 efficiently structured: purpose first, constraint second, return value third. No redundant information despite the null title field.

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?

For a single-parameter tool without annotations or output schema, the description compensates well by documenting the business rule (parking requirement) and return structure, though it could mention irreversibility.

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?

With 100% schema coverage, the baseline is 3. The description does not add additional semantic detail about the reservation_id parameter beyond what the schema already provides ('The active reservation ID to end').

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 opens with the specific verb 'End' and clearly identifies the resource as an 'active Zipcar rental session,' distinguishing it from siblings like extend_reservation or reserve_car.

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?

Provides critical prerequisite context ('The car must be parked at a valid Zipcar spot') indicating when the tool can successfully execute, though it doesn't explicitly contrast usage with extend_reservation.

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