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arc-control-mcp

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JavaScript
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Scroll

scroll
Idempotent

Move the page up, down, to top, or bottom, or bring an element into view. Returns vertical position, page height, and viewport to show remaining content.

Instructions

Scroll the page, or scroll an element into view. Page scrolls report scrollY, pageHeight and viewport, so you can tell how much is left.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
exactNoFor "text=", "label=" and "placeholder=" selectors, require the whole trimmed text to equal the label instead of containing it. No effect on CSS, ref= or role= selectors.
amountNoPixels to scroll for up and down
tab_idNoArc tab id from list_tabs. Omit to use this agent's current tab. A tool that changes a tab will not fall back to the tab the user is looking at, so pass this or call open_url first.
verboseNoInclude the bulky element rect and longer attribute values
selectorNoScroll this element into view instead of scrolling the page. CSS selector, "text=Label" (substring, exact matches ranked first), "ref=e12", "role=button[name="Save"]", "label=Email" or "placeholder=Search".
directionNoPage scroll directiondown

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv0.4.0
    • changedInput schema / properties / exact / description
      Previous value: -"For \"text=\" selectors, require the whole trimmed text to equal the label instead of containing it. No effect on CSS selectors."New value: +"For \"text=\", \"label=\" and \"placeholder=\" selectors, require the whole trimmed text to equal the label instead of containing it. No effect on CSS, ref= or role= selectors."
    • changedInput schema / properties / selector / description
      Previous value: -"Scroll this element into view instead of scrolling the page. CSS selector, or \"text=Label\" (substring, exact matches ranked first)."New value: +"Scroll this element into view instead of scrolling the page. CSS selector, \"text=Label\" (substring, exact matches ranked first), \"ref=e12\", \"role=button[name=\"Save\"]\", \"label=Email\" or \"placeholder=Search\"."
    • changedInput schema / properties / tab_id / description
      Previous value: -"Arc tab id from list_tabs. Omit to use this agent's current tab, falling back to whatever tab is active in Arc."New value: +"Arc tab id from list_tabs. Omit to use this agent's current tab. A tool that changes a tab will not fall back to the tab the user is looking at, so pass this or call open_url first."
  2. First observedv0.3.0

TDQS

A3.8/5.0
Behavior4/5

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

Annotations already declare the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false, openWorldHint=true). The description adds genuinely useful behavioral detail by disclosing that page scrolls return scrollY, pageHeight and viewport, which matters because there is no output schema. It doesn't explain why the operation is flagged non-read-only, so it's strong but not complete.

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 tight sentences with no filler. The core action is front-loaded and the return-value note is secondary, so an agent gets the essential information first.

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 no output schema, the description usefully compensates by naming the returned scroll metrics. All parameters are covered by the schema and the safety profile by annotations, so nothing critical is missing, though the tab_id fallback caveat is left entirely to the schema.

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%, so all six parameters (selector, direction, amount, exact, tab_id, verbose) are already documented in the schema. The description only restates the page-versus-element distinction that the selector parameter already conveys, adding no syntax or format detail beyond the schema. Baseline 3 is appropriate.

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) and resource (page or element), and explicitly separates the two operating modes: page scrolling versus scrolling an element into view. It is immediately clear what the tool does, though it doesn't explicitly differentiate itself from any sibling since no sibling overlaps this behavior.

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 via the return-value note ('so you can tell how much is left'), suggesting it's used for pagination-style navigation, but it never states when to prefer scroll over alternatives or any preconditions. Usage is inferable but not guided.

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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