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compare_element_alignment

Read-only

Compare alignment and dimensions of two web elements. Checks edge and center alignment, width, and height, showing pass/fail and pixel differences for debugging layout issues.

Instructions

COMPARE TWO ELEMENTS: Get comprehensive alignment and dimension comparison in one call. Shows edge alignment (top, left, right, bottom), center alignment (horizontal, vertical), and dimensions (width, height). Perfect for debugging 'are these headers aligned?' or 'do these panels match?'. Returns all alignment info with ✓/✗ symbols and pixel differences. For parent-child centering, use inspect_dom() instead (automatically shows if children are centered in parent). More efficient than evaluate() with manual getBoundingClientRect() calculations.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
selector1YesCSS selector, text selector, or testid shorthand for the first element (e.g., 'testid:main-header', '#header')
selector2YesCSS selector, text selector, or testid shorthand for the second element (e.g., 'testid:chat-header', '#secondary-header')
Behavior4/5

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

Annotations indicate read-only. Description adds transparency by detailing output format (✓/✗ symbols and pixel differences), beyond what annotations provide.

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?

Description is concise (three sentences), front-loaded with purpose in bold, and efficiently includes usage guidance and output details.

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?

No output schema, but description explains output content (symbols, pixel differences) and use cases. For a simple tool with two parameters, it is complete.

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 has 100% coverage with parameter descriptions. The description does not add significant extra semantics beyond the schema, but it provides context for the parameters' role in alignment comparison.

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 states the tool's function: comparing two elements for alignment and dimensions. It lists specific attributes (edge alignment, center alignment, dimensions) and distinguishes from siblings like inspect_dom and evaluate.

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?

Explicitly provides when to use (debugging alignment) and when not to (parent-child centering, refer to inspect_dom). Also notes efficiency over evaluate().

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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