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Mochi

Mochi

by DevZonayed
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JavaScript
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browser_emulate_viewport

Emulate device viewport, DPR, mobile mode, and user agent via CDP presets or custom width/height for responsive testing.

Instructions

Programmatic Device Mode via CDP (viewport + DPR + mobile/UA). Preset or width/height.

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": "browser_emulate_viewport"
  }
}

Input Schema

NameRequiredDescriptionDefault
presetNo
widthNo
heightNo
deviceScaleFactorNo
mobileNo
userAgentNo
tabIdNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

B3.3/5.0
Behavior2/5

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

No annotations are provided. The description lacks behavioral details such as persistence across tabs, side effects, or relationship to other emulation states. It only states 'Programmatic Device Mode via CDP' without deeper transparency.

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 very concise with two sentences, front-loading the key purpose and options. No wasted words.

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 7 parameters and no output schema or annotations, the description is far too brief. It omits critical context like parameter meanings (e.g., tabId, deviceScaleFactor) and does not specify return behavior.

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?

The description briefly mentions 'Preset or width/height' but does not explain the other 5 parameters (deviceScaleFactor, mobile, userAgent, tabId). With 0% schema description coverage, the description should compensate but fails to do so.

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 tool's function: programmatic device mode via CDP, covering viewport, DPR, mobile, and user-agent. It mentions presets and custom width/height, which distinguishes it from siblings like browser_clear_emulation and browser_window_resize.

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 usage for viewport emulation but does not explicitly guide when to use this vs alternatives (e.g., browser_window_resize for actual window resizing) or when not to use it.

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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