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Browser MCP

by drisplabs
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Scroll

scroll

Move the viewport up or down by a pixel amount to reveal more of a long page or trigger lazy-loaded content. Returns a page snapshot with the new position.

Instructions

Scroll the viewport up or down by a pixel amount. Use to reveal more of a long page or trigger lazy-loaded content; use scroll_to when you know the target element. Returns a fresh page snapshot reflecting the new scroll position.

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": {
      "direction": "<direction>"
    },
    "name": "scroll"
  }
}

Input Schema

NameRequiredDescriptionDefault
amountNoDistance to scroll in pixels (default: 500).
page_idNoPage ID. If omitted, operates on the most recently used page.
directionYesDirection to scroll the viewport: 'up' or 'down'.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • addedInput schema / properties / amount / description
      Added value: +"Distance to scroll in pixels (default: 500)."
    • addedInput schema / properties / direction / description
      Added value: +"Direction to scroll the viewport: 'up' or 'down'."
    • addedInput schema / properties / page_id / description
      Added value: +"Page ID. If omitted, operates on the most recently used page."
  2. First observedv4.6.4

TDQS

A4.5/5.0
Behavior4/5

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

Since no annotations are provided, the description bears full responsibility. It discloses the return value ('Returns a fresh page snapshot reflecting the new scroll position'), which is valuable. However, it does not explicitly mention whether the operation is idempotent or whether there are any side effects beyond the scroll and snapshot. Still, for a simple scroll action, this is reasonably transparent.

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 extremely concise with three sentences that front-load the essential purpose, usage guidance, and return value. Every sentence adds value without redundancy.

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 tool with three parameters (one required), no output schema, and a simple scroll functionality, the description provides all necessary information: what it does, when to use it, how it differs from a sibling, and what it returns. It is complete for its complexity level.

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?

The input schema has 100% coverage, so the schema itself documents each parameter. The description adds context like 'pixel amount' and 'trigger lazy-loaded content' but does not significantly enhance parameter understanding 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 specifies the verb ('scroll'), the resource ('viewport'), and the manner ('up or down by a pixel amount'). It also distinguishes the tool from the sibling 'scroll_to' by stating when to use which, making its purpose unambiguous.

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?

The description explicitly states when to use this tool ('to reveal more of a long page or trigger lazy-loaded content') and when not to ('use scroll_to when you know the target element'), providing clear context and an alternative.

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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