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Browser Session MCP

by xav-ie
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Rust
Local

move_mouse

Move the cursor to viewport coordinates in the active tab to trigger hover, mouseover and mousemove handlers, enabling hover menus and tooltips before reading or clicking them.

Instructions

Move the mouse to viewport coordinates x,y (CSS pixels from the top-left) in the session's active tab via CDP input (trusted move event), so the page's hover, mouseover and mousemove handlers fire. Use it to open hover menus and tooltips before reading or clicking them, and to add human-like behavioral telemetry. Don't use it to click, drag or scroll: use click and scroll. Coordinates outside the viewport are not rejected; the move just hovers nothing. Returns a confirmation with the position.

Input Schema

NameRequiredDescriptionDefault
xYesHorizontal position from the viewport's left edge in CSS pixels.
yYesVertical position from the viewport's top edge in CSS pixels.
sessionIdYesThe id returned by open_browser_session. Errors if no open session has it.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • addedInput schema / properties / sessionId / description
      Added value: +"The id returned by open_browser_session. Errors if no open session has it."
    • addedInput schema / properties / x / description
      Added value: +"Horizontal position from the viewport's left edge in CSS pixels."
    • addedInput schema / properties / y / description
      Added value: +"Vertical position from the viewport's top edge in CSS pixels."
  2. First observedv0.1.2

TDQS

A4.6/5.0
Behavior4/5

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

Adds real context beyond the annotations: the move is a trusted CDP input event that fires hover/mouseover/mousemove handlers, out-of-viewport coordinates are silently accepted and hover nothing, and the call returns a confirmation with the position. The non-rejection of out-of-range values is a genuinely useful non-obvious behavior. It does not state error conditions beyond the session lookup (already in schema) or whether the page is scrolled/waited on.

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?

Front-loaded with the core action and coordinates, then usage, then exclusions and edge-case behavior. Every clause carries information, though the first sentence is dense with parentheticals stacked back to back.

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

Completeness5/5

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

For a 3-parameter tool with no output schema, the definition covers action, coordinate semantics, side effects on page handlers, out-of-bounds behavior, exclusions, and the return value shape. Nothing an agent needs in order to call it correctly is missing.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3; the description earns above baseline by clarifying the coordinate origin (top-left of the viewport), the unit (CSS pixels), and what happens when coordinates fall outside the viewport. Minor remaining ambiguity: behavior with fractional or negative coordinates is left implicit.

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?

States a specific verb (move) and resource (the mouse) with precise scope: viewport CSS pixel coordinates in the session's active tab via CDP input. It distinguishes itself from click/scroll siblings by naming them, so an agent can route correctly without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives positive use cases (open hover menus and tooltips before reading or clicking them, add human-like telemetry) and an explicit exclusion with the alternative named: 'Don't use it to click, drag or scroll: use click and scroll.' Both when and when-not are covered with a concrete routing rule.

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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