MBTA MCP Server

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mbta_get_vehicles

Retrieve real-time positions of MBTA vehicles, filtered by route, trip, or specific vehicle ID, with configurable result limits.

Instructions

Get real-time MBTA vehicle positions.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "mbta_get_vehicles"
  }
}

Input Schema

Name	Required	Description
`vehicle_id`	No	Specific vehicle ID to get
`route_id`	No	Filter vehicles by route ID
`trip_id`	No	Filter vehicles by trip ID
`page_limit`	No	Number of results to return (default: 10)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0May 26, 2026

TDQS

B3.2/5.0

Behavior2/5

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

No annotations exist, so the description must handle behavioral disclosure, but it only states the purpose. It omits important traits like data freshness, authentication, rate limits, or pagination behavior (despite a page_limit parameter). The user cannot infer real-time update frequency or how results are ordered.

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?

The description is a single, concise sentence that immediately communicates the core function. No unnecessary words, and it is front-loaded with the key action and resource.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 4 optional parameters and no output schema, the description is incomplete. It fails to explain return format, field names, or how to use filters effectively. A real-time data tool requires more context for proper usage.

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 descriptions cover 100% of parameters with basic explanations. The tool description adds no additional value beyond what the schema already provides. Baseline 3 is appropriate.

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 action ('Get'), the resource ('real-time MBTA vehicle positions'), and is specific. It distinguishes this tool from siblings like mbta_get_predictions or mbta_get_routes by focusing on vehicle position data.

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. It does not mention context, prerequisites, or exclusions, such as when to prefer mbta_get_predictions or mbta_get_schedules instead.

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