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umbra

umbra

by lxchx
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Remote

Scroll

scroll

Move a tab’s viewport by pixel offsets, jump to the bottom, or bring a selector into view to lazy-load or reveal page content.

Instructions

Scroll by (dx,dy), to_bottom=True, or scrollIntoView selector. Lazy-load / reveal.

Ex: scroll('t0', to_bottom=True) / scroll('t0', selector='#footer') → {"ok":true}

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

Input Schema

NameRequiredDescriptionDefault
dxNo
dyNo
tab_idYes
selectorNo
to_bottomNo

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.7/5.0
Behavior3/5

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

No annotations, so the description carries the burden. It does disclose the mode semantics and the example return shape {"ok":true}, but says nothing about whether scrolling waits for lazy-loaded content to settle, smooth vs instant scrolling, or error behavior when the selector is missing.

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?

Two short lines: modes and intent first, then two runnable examples with the return value. Every token earns its place, no filler.

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

Completeness4/5

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

With an output schema present the description needn't explain returns, and it covers all three usage modes plus a sample response. The remaining gap is behavioral (waiting on lazy loads, failure modes), which is not critical for a simple scroll call.

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 description coverage is 0%, so the description must compensate and largely does: it explains dx/dy deltas, the to_bottom flag, and selector-based scrollIntoView with concrete example values, including the non-obvious default of dy=600 implied by the delta mode. Only tab_id is left unremarked.

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?

States a specific verb (scroll) with the three operating modes (delta, to_bottom, selector) and the motivation 'Lazy-load / reveal'. Clearly distinguishable from siblings like navigate or click_at, though it doesn't name a nearest alternative.

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?

'Lazy-load / reveal' implies the reason to scroll, and the two examples show typical invocation. There is no explicit when-not guidance or comparison to other viewport-affecting tools, leaving usage inferred.

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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