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emulate

Simulates device viewports, user agents, color schemes, geolocation, headers, and network/CPU throttling on a target page to test varied browser conditions.

Instructions

Emulates various features on the target page.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pageIdYesTargets a specific page by ID.
viewportNoEmulate device viewports '<width>x<height>x<devicePixelRatio>[,mobile][,touch][,landscape]'. 'touch' and 'mobile' to emulate mobile devices. 'landscape' to emulate landscape mode.
userAgentNoUser agent to emulate. Set to empty string to clear the user agent override.
colorSchemeNoEmulate the dark or the light mode. Set to "auto" to reset to the default.
geolocationNoGeolocation (`<latitude>,<longitude>`) to emulate. Latitude between -90 and 90. Longitude between -180 and 180. Omit to clear the geolocation override.
extraHttpHeadersNoExtra HTTP headers as a JSON string object, e.g. {"X-Custom": "value", "Authorization": "Bearer token"}. Headers are included into every HTTP request originating from the page and persist across navigations until cleared. Pass an empty string to clear all extra headers.
cpuThrottlingRateNoRepresents the CPU slowdown factor. Omit or set the rate to 1 to disable throttling
networkConditionsNoThrottle network. Omit to disable throttling.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

C2.3/5.0
Behavior2/5

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

Annotations declare readOnlyHint=false, so this mutates page state, but the description says nothing about persistence, scope, or reversibility. It does not repeat or contradict the annotation, but it also adds no behavioral context beyond what the schema itself hints at.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single short sentence, so it is front-loaded and free of waste, but its brevity comes from under-specification rather than discipline. Structure is acceptable; content is thin.

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?

For an 8-parameter tool that persistently overrides page behavior across navigations, the description leaves the agent without any sense of scope or side effects. With no output schema and only a null readOnlyHint annotation, the description should carry more of the load.

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% and the parameter docs are unusually rich (clearing overrides, geolocation ranges, header format), so the baseline of 3 applies. The description contributes nothing to parameter meaning beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose2/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description restates the tool name almost literally ('emulate' → 'Emulates various features'), which is close to a tautology. It never names which features (viewport, user agent, geolocation, network throttling) despite the schema enumerating them, so an agent cannot distinguish it from siblings like resize_page or navigate_page without opening the schema.

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?

There is no when-to-use guidance, no mention of prerequisites (does a page need to exist first?), and no routing to or away from any sibling tool. The agent must infer the entire usage context from the parameter list.

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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