Zipcar MCP Server

Server Quality Checklist

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Latest release: v1.0.0
Disambiguation5/5
Each tool has a clearly distinct purpose with no overlap: end_trip handles active rentals, extend_reservation modifies existing bookings, get_car_details provides vehicle info, get_reservation_history accesses past/future bookings, reserve_car creates new reservations, and search_cars finds available vehicles. The descriptions reinforce these distinct roles, making misselection unlikely.
Naming Consistency5/5
All tool names follow a consistent verb_noun pattern (e.g., end_trip, extend_reservation, get_car_details), using clear action verbs paired with specific nouns. There are no deviations in style or convention, making the set predictable and easy to understand at a glance.
Tool Count5/5
With 6 tools, this server is well-scoped for managing Zipcar rentals, covering key workflows like searching, reserving, extending, ending trips, and accessing details/history. Each tool earns its place without redundancy, and the count is typical for a focused domain like car-sharing services.
Completeness5/5
The tool set provides complete coverage for the Zipcar rental lifecycle: search_cars and get_car_details for discovery, reserve_car and extend_reservation for booking management, end_trip for session closure, and get_reservation_history for tracking. There are no obvious gaps, enabling agents to handle end-to-end tasks without dead ends.
Average 3.6/5 across 6 of 6 tools scored.
See the Tool Scores section below for per-tool breakdowns.
- No community issues in the last 6 months
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How is the quality score calculated?

The overall quality score combines two components: Tool Definition Quality (70%) and Server Coherence (30%).

Tool Definition Quality measures how well each tool describes itself to AI agents. Every tool is scored 1–5 across six dimensions: Purpose Clarity (25%), Usage Guidelines (20%), Behavioral Transparency (20%), Parameter Semantics (15%), Conciseness & Structure (10%), and Contextual Completeness (10%). The server-level definition quality score is calculated as 60% mean TDQS + 40% minimum TDQS, so a single poorly described tool pulls the score down.

Server Coherence evaluates how well the tools work together as a set, scoring four dimensions equally: Disambiguation (can agents tell tools apart?), Naming Consistency, Tool Count Appropriateness, and Completeness (are there gaps in the tool surface?).

Tiers are derived from the overall score: A (≥3.5), B (≥3.0), C (≥2.0), D (≥1.0), F (<1.0). B and above is considered passing.

Tool Scores

Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It partially compensates by disclosing what data fields are returned (addressing the lack of an output schema), but it fails to declare whether this is a safe read-only operation, if it requires authentication, or if there are rate limits.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, front-loaded sentence that efficiently communicates the tool's purpose and return value. The field enumeration is valuable given the lack of an output schema, though it makes the sentence slightly dense.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple single-parameter lookup tool with no annotations and no output schema, the description is reasonably complete. It compensates for the missing output schema by listing the specific data fields returned, providing the agent with adequate expectations of the tool's utility.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 100% description coverage for the car_id parameter ('The Zipcar vehicle ID from search results'). The tool description adds no additional parameter context, but the high schema coverage establishes the baseline score of 3.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose4/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool retrieves 'detailed information about a specific Zipcar' and enumerates specific fields returned (vehicle type, features, seating, fuel type, pricing rates). The phrase 'specific Zipcar' distinguishes it from the sibling search_cars tool, though it does not explicitly name the sibling.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines2/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives like search_cars or reserve_car. It does not mention that this requires a car_id typically obtained from search results (though the parameter schema description does hint at this).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior2/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of behavioral disclosure. While it mentions the filtering capability, it fails to disclose critical behavioral traits: it does not confirm this is a read-only operation (safe, non-destructive), does not describe the return format or structure of reservation data, and does not mention error conditions (e.g., if no reservations exist).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description consists of two short sentences totaling 11 words. It is appropriately front-loaded with the primary action ('View past and upcoming Zipcar reservations') followed by secondary filtering details. The second sentence is slightly redundant with the schema's enum descriptions, but overall it is efficient with minimal waste.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness3/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool has only two parameters with 100% schema coverage and no output schema, the description provides the minimum viable context for an AI agent to understand the tool's basic function. However, given the absence of annotations and output schema, the description should ideally disclose the read-only nature and general return value type to be fully complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 100% description coverage for both parameters ('filter' enum values and 'limit' purpose). The description mentions filtering by upcoming/past, which aligns with the schema but adds no additional semantic context, examples, or usage guidance beyond what the structured schema already provides. Baseline score applies.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose4/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool 'View[s] past and upcoming Zipcar reservations,' providing a specific verb and resource. However, it does not explicitly differentiate this tool from sibling tools like 'reserve_car' or 'extend_reservation' (e.g., stating this is for viewing existing reservations rather than modifying them).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description mentions filtering capabilities ('Can filter by upcoming or past reservations'), implying when different filter values might be used. However, it lacks explicit guidance on when to use this tool versus alternatives like 'search_cars' or 'get_car_details', and does not mention prerequisites such as authentication requirements.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden. It successfully discloses the availability validation constraint but omits other behavioral traits such as idempotency, failure modes when the car is unavailable, payment implications, or whether extensions can be partial vs. only end-time extensions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Optimal length at two sentences. The first sentence front-loads the core action, while the second provides essential constraint information without redundancy. No filler or tautology present.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness3/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Adequate for a two-parameter mutation tool, covering the primary function and key business constraint. However, given zero annotations and no output schema, it lacks completeness on error states, side effects (billing), and success indicators that would help an agent handle the response.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, documenting both 'reservation_id' and 'new_end_time' (including ISO 8601 format). The tool description adds no parameter-specific details, but per rubric guidelines, high schema coverage establishes a baseline of 3.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose4/5
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states the specific action (extend) and resource (existing Zipcar reservation), distinguishing it from sibling 'reserve_car' by emphasizing 'existing.' The scope (to a later end time) is precise, though it could explicitly contrast with 'end_trip' for maximum clarity.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Provides a critical usage constraint (car must be available for extended period), which implies when the tool will fail. However, it lacks explicit guidance on when to choose this over 'reserve_car' for overlapping times or whether extensions incur additional charges.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden. It discloses the return structure ('list of available vehicles with rates and locations') and filtering behavior (availability check). However, it omits operational details like rate limits, error handling when no cars are found, or whether the operation is idempotent/safe.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two efficiently constructed sentences. The first front-loads the action and scope; the second explains the return value (critical given no output schema exists). No redundant words or tautology.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the simple 4-parameter input with complete schema coverage and no output schema, the description adequately compensates by describing the return values. It could be improved by explicitly stating this is a read-only operation (since annotations are absent), but it is sufficiently complete for tool selection.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Input schema has 100% description coverage with clear examples (ISO 8601 formats, address formats). The description reinforces semantics by grouping start_time/end_time as a 'time period' and location as a proximity search anchor, but does not add significant meaning beyond what the schema already provides.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description uses the specific verb 'Search' with the resource 'available Zipcars' and clarifies the scope ('near a location for a given time period'). It effectively distinguishes this from siblings like 'reserve_car' (booking) and 'get_car_details' (specific vehicle info) by emphasizing availability and location-based listing.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies this is a pre-reservation step by mentioning 'available' vehicles and returning a list, suggesting it precedes 'reserve_car'. However, it lacks explicit guidance on when to use this versus 'get_car_details' or explicit sequencing instructions (e.g., 'use this before reserving').
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior3/5
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.
Conciseness5/5
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.
Completeness4/5
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.
Parameters3/5
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.
Purpose5/5
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.
Usage Guidelines4/5
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.
Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of behavioral disclosure. It successfully notes the authentication requirement and return value ('Returns reservation confirmation details'), but omits other critical behavioral traits for a mutation tool: error handling (what if the time slot is unavailable?), idempotency, side effects (payment processing), or rate limits.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Three sentences with zero waste: purpose ('Book a Zipcar...'), prerequisite ('Requires...'), and output ('Returns...'). Information is front-loaded with the action verb first, making it immediately scannable.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the moderate complexity (4 flat parameters) and lack of output schema or annotations, the description adequately compensates by stating the return value type and authentication needs. It could be improved by mentioning error conditions or sibling workflow (e.g., search before reserve), but covers the essentials for invocation.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, documenting all four parameters including ISO 8601 format for timestamps and optional values. The description references 'specific time slot' which loosely maps to the time parameters, but adds no semantic meaning beyond what the schema already provides, warranting the baseline score.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'Book', the resource 'Zipcar', and the scope 'specific time slot'. It effectively distinguishes from siblings: unlike search_cars (which finds vehicles), get_car_details (which retrieves info), or extend_reservation (which modifies existing bookings), this tool creates new reservations.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides clear prerequisite context ('Requires the user to be logged in to Zipcar'), establishing when the tool can be used. However, it lacks explicit guidance on alternatives (e.g., 'use search_cars first to obtain car_id') or exclusion conditions (e.g., conflicting reservations).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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