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TypeScript
Hybrid

Compare Page States

compare
Read-onlyIdempotent

Diff two webpage states or PNG captures to get before, after, and mismatch metrics for QA and visual regression testing.

Instructions

Compare two live webpage states or two PNG captures and return before, after, diff, plus mismatch metrics. Useful for QA, release review, and visual regression workflows.

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": {
      "before": "<before>",
      "after": "<after>"
    },
    "name": "compare"
  }
}

Input Schema

NameRequiredDescriptionDefault
afterYes
beforeYes
thresholdNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

A4.2/5.0
Behavior4/5

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

Annotations already provide readOnlyHint, openWorldHint, and idempotentHint. The description adds value by explaining that it accepts live webpage states or PNG captures and returns before/after/diff/metrics, which is not covered by annotations. No contradiction is present.

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 exactly two sentences, front-loaded with the core purpose and followed by use cases. Every word contributes, with no repetition or fluff.

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?

Despite the nested object complexity and lack of output schema, the description covers the main function and return value structure. Strong annotations compensate for safety, but the description would benefit from explaining threshold and capture sub-properties to be fully self-sufficient.

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 0%, so the description must compensate. It clarifies that 'before' and 'after' can be either live URLs or PNG captures, but it does not explain the 'threshold' parameter or the many sub-properties like hide, delay, width, etc., leaving gaps in understanding.

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 explicitly states 'Compare two live webpage states or two PNG captures and return before, after, diff, plus mismatch metrics.' This clearly identifies the verb (compare), the resource (two webpage states or PNG captures), and the outputs, distinguishing it from sibling tools like 'screenshot' and 'analyze'.

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

Usage Guidelines4/5

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

The description says 'Useful for QA, release review, and visual regression workflows,' which provides clear contexts for when to use the tool. However, it does not explicitly mention when not to use it or contrast it with alternatives, so it falls short of a 5.

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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