accessibility-mcp-server

check_images_alt

Checks all images on a web page for missing alt text to verify WCAG 1.1.1 compliance. Returns each image with its alt text status.

Instructions

Prueft alle Bilder einer Webseite auf Alt-Text (WCAG 1.1.1).

Args: url: Zu pruefende URL

Returns: Alle Bilder mit Alt-Text-Status

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": {
      "url": "<url>"
    },
    "name": "check_images_alt"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0May 29, 2026

TDQS

B3.3/5.0

Behavior2/5

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

No annotations are provided, so the description carries the full burden. It only states that the tool 'checks' images for alt text without disclosing any behavioral traits such as network requests, rate limits, or what constitutes a check (e.g., does it parse the page asynchronously?). This is insufficient for a tool with no built-in safety cues.

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 very short and direct, with separate lines for Args and Returns. No unnecessary words. However, the absence of any explanatory detail beyond the basics slightly reduces the score from a perfect 5.

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

Completeness3/5

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

Given that an output schema exists, the tool does not need to detail return values. However, the description lacks information about the depth of the check, edge cases (e.g., images without alt attribute vs empty alt), or whether it follows the page's redirects. It is minimally complete for a simple tool but leaves gaps.

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

Parameters2/5

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

There is only one parameter (url), and the description repeats its name and a generic phrase ('Zu pruefende URL') which adds no meaning beyond the input schema. With 0% schema description coverage, the description fails to provide any additional context about the expected format or constraints of the URL.

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 checks all images on a webpage for alt text, referencing WCAG 1.1.1. It is specific about the verb (prueft) and resource (Bilder einer Webseite) and distinguishes from sibling tools that focus on other accessibility checks.

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 does not explicitly state when to use this tool versus alternatives like check_color_contrast or check_heading_structure. While the name and context hint at its specific purpose, there is no guidance on prerequisites or situations where it should be avoided.

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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