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emulator-mcp

emulator-mcp

by damipineda
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JavaScript
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open_responsive_session

Open one URL across multiple device viewports, preserve each page state between calls, and return a dashboard link for side-by-side screenshots updated every 3 seconds.

Instructions

Abre la MISMA URL en varios tamaños y mantiene las paginas entre llamadas MCP. Devuelve sessionId, screenIds y dashboardUrl: abre ese enlace para ver capturas lado a lado actualizadas cada 3 segundos. Cada pantalla mantiene su propio estado web. No requiere iframes ni quitar cabeceras de seguridad.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "<url>"
    },
    "name": "open_responsive_session"
  }
}

Input Schema

NameRequiredDescriptionDefault
urlYes
localeNo
devicesNo
colorSchemeNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.2.1

TDQS

B3.4/5.0
Behavior4/5

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

Annotations only say readOnlyHint=false and openWorldHint=true, so the description carries real weight and delivers: pages persist between MCP calls, each screen keeps independent web state, screenshots refresh every 3 seconds, and no iframes or security-header stripping are needed. These are meaningful behavioral traits beyond the annotations, though it omits resource/lifecycle limits (e.g. max sessions, cleanup).

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 core action and its payoff (dashboardUrl with live side-by-side screenshots) are front-loaded, and each sentence adds information. It is dense but not padded, though the trailing note about iframes/headers is somewhat incidental.

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?

There is no output schema, and the description usefully enumerates the return values (sessionId, screenIds, dashboardUrl), which covers the response side. But for a stateful, mutating session-creating tool, the undocumented input parameters leave a clear gap in what an agent needs to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0% across four parameters, and the description does not compensate: url, locale, devices (array, 1-6 items) and colorScheme are never explained. 'Various sizes' only loosely gestures at devices, leaving the agent to infer the meaning and format of every input.

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 states a specific verb and resource: it opens the same URL at multiple viewport sizes and creates a persistent session, returning sessionId, screenIds and a dashboardUrl. This is clear enough for an agent to distinguish it from list/observe/navigate siblings, though it does not explicitly name an alternative it is not.

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?

Usage is implied (open a session first, then pages persist across MCP calls), and it hints at the advantage over one-off screenshot tools. However it never states when to prefer it over siblings like check_responsive, preview_devices or screenshot_on, nor any prerequisites.

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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