Open source · MIT licensed

mcp-web-validator — technical on-page SEO & W3C validator.

Audit one authorized public HTML page or validate supplied HTML and CSS in ChatGPT, then use the open-source local MCP for file-based audits and responsive screenshots.

View on GitHub Setup Configuration

ChatGPT tools: 7
Local tools: 8
Audit layers: 5
License: MIT

mcp-web-validator overview with HTML, link, JSON-LD, and technical validation checks — mcp-web-validator combines HTML, link, JSON-LD, and technical validation in one MCP workflow.

About

What is mcp-web-validator?

mcp-web-validator is an open-source Model Context Protocol (MCP) server that helps AI assistants validate W3C HTML and CSS syntax, parse JSON-LD syntax, check link integrity, and capture layout screenshots in multiple viewports.

AI agents generate a large amount of code, but they need a feedback loop to verify the output. Web Validator provides a public ChatGPT app for markup you explicitly provide or one authorized public HTML page, plus a separate local MCP for workspace files.

The public ChatGPT app is read-only: it never accesses your filesystem or creates files. A public-page audit fetches one authorized HTML document and sends the fetched HTML to the Nu HTML Checker hosted at html5.validator.nu; SEO and JSON-LD checks run locally in the DigestSEO Worker. Optional link checking contacts at most 20 links. The hosted app does not execute JavaScript, crawl a site, fetch linked CSS, or authenticate to private pages. The local MCP remains available for desktop workflows that need filesystem access or responsive screenshots.

Tools

Public ChatGPT capabilities

Seven read-only tools designed for the public ChatGPT app. Submit only markup and public URLs you are authorized to share or inspect.

01 validate_html

Validates HTML you provide with the Nu HTML Checker hosted at html5.validator.nu.

02 audit_public_webpage

Fetches one authorized public HTML page, sends its HTML to the Nu checker, and runs local SEO and JSON-LD checks. Optional link checking is capped at 20 links.

03 validate_css

Parses CSS you provide locally and reports syntax errors.

04 audit_seo_metadata

Audits titles, descriptions, headings, image alt text, canonical tags, viewport tags, and Open Graph metadata.

05 check_broken_links

Checks a capped set of authorized public links found in supplied HTML without following redirects.

06 validate_schema_markup

Identifies JSON-LD blocks in supplied HTML and reports JSON syntax errors.

07 generate_validation_report

Combines W3C validation with SEO and JSON-LD checks into a concise report.

ChatGPT app

Use it in ChatGPT without local filesystem access

Install Web Validator by DigestSEO from the ChatGPT App Directory once it is available in your region. Provide HTML or CSS, or ask it to audit one authorized public webpage. A webpage audit checks the fetched HTML, technical SEO, and JSON-LD, with optional link checking capped at 20 links; it does not execute JavaScript, crawl the site, fetch linked CSS, or sign in. See the privacy policy for the data flow or visit support.

Setup

Configure the local MCP in your IDE

Claude Desktop

Add this to your claude_desktop_config.json:

{
  "mcpServers": {
    "mcp-web-validator": {
      "command": "npx",
      "args": ["-y", "mcp-web-validator"]
    }
  }
}

Cursor

Navigate to Settings > Features > MCP and add:

Name: mcp-web-validator
Type: command
Command: npx -y mcp-web-validator

CLI Execution

Run audits directly from the console

~/mcp-web-validator

npm install -g mcp-web-validator
# Or execute on the fly with npx:
npx -y mcp-web-validator

Star the repo and improve your local AI coding loop today.

MIT licensed. Full W3C compliance & technical SEO audits.

View on GitHub