ui-diff-mcp

compare_ui_images

Compare a design mockup against a real mobile screenshot to pinpoint visual mismatches through deterministic pixel comparison.

Instructions

Compares an expected mobile mockup image against an actual mobile screenshot using only deterministic methods (no visual models).

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": {
      "expectedImagePath": "<expectedImagePath>",
      "actualImagePath": "<actualImagePath>"
    },
    "name": "compare_ui_images"
  }
}

Input Schema

Name	Required	Default
`mode`	No	free
`runLabel`	No
`projectRoot`	No
`actualImagePath`	Yes
`expectedImagePath`	Yes

Output Schema

Name	Required	Default
`runId`	Yes
`status`	Yes
`summary`	Yes
`warnings`	Yes
`diffCount`	Yes
`auditScope`	No
`reportPath`	Yes
`artifactRoot`	Yes
`auditLimited`	Yes
`debugSummary`	No
`runArtifacts`	Yes
`recoverySummary`	No
`locatorCoverageStatus`	Yes	not_run
`unresolvedRegionCount`	Yes
`visualClassificationStatus`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Jun 30, 2026

TDQS

C2.6/5.0

Behavior2/5

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

With no annotations, the description must cover behavioral traits. It states 'deterministic methods' and 'no visual models', but omits side effects, permissions, performance, or behavior on mismatched images.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single concise sentence that immediately states the action. However, it sacrifices completeness for brevity, lacking structure to cover parameters or context.

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

Completeness2/5

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

Given 5 parameters, an output schema, and sibling tools indicating a workflow, the description is insufficient. It doesn't explain the role of parameters or how this fits into the larger tool suite.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters1/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 5 parameters including an enum for 'mode', but the description gives no information about any parameter. With 0% schema description coverage, this is a critical gap.

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?

The description clearly states the tool compares expected and actual mobile images using deterministic methods. It does not explicitly differentiate from sibling tools like 'discover_ui_diffs' or 'start_ui_diff_run', but the mention of 'no visual models' hints at its specificity.

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

Usage Guidelines2/5

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

The description only notes that it uses deterministic methods, implying a use case where visual models are not wanted. No guidance on when to use this over siblings or prerequisites (e.g., captured images). Lacks explicit context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server