REA
Reverse engineer anything from your terminal or agent with one CLI and MCP server.
Runs on your computer
Validatehtml
Overview
Description from the maker (original English)
Validate HTML, CSS, JSON, XML and WCAG accessibility from an AI coding agent. No key needed.
PopNx MCP’s three pillars
These three are never merged into one score: opinions, measurements and popularity are different things.
- User voiceiNo reviews yetReviews open together with accounts in a later step
- Our basic checksi1 of 1 passedChecked from public information; code not scanned yet
- UsageiEarly↓ 368/wk · ★ –
What you can do with it
We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.
- Connection: Runs on your computer
- Transport: stdio
- Category: Developer tools
- You need to fill in: VALIDATEHTML_API_KEY
Install
Pick the AI app you use, then copy the settings.
Before you install
- Basic checks: 1 of 1 passed
- Runs on your computer with your user’s permissions (files, network, apps).
- You fill in yourself:
VALIDATEHTML_API_KEY
Values marked secret are keys to your account. Never share them or paste them into a chat.
You need
- npmNode.js installed (for the npx command)
Which app do you use?
Pick your app above. We remember it, so next time the button says “Install in …”.
Open Claude Desktop → Settings → Developer → Edit Config, and paste this into claude_desktop_config.json
{
"mcpServers": {
"validatehtml": {
"command": "npx",
"args": [
"-y",
"validatehtml",
"mcp"
],
"env": {
"VALIDATEHTML_API_KEY": "your-value"
}
}
}
}Run this in your terminal
claude mcp add validatehtml --env VALIDATEHTML_API_KEY=your-value -- npx -y validatehtml mcpFill in the empty values before running it.
Or copy the settings yourself
Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json
{
"mcpServers": {
"validatehtml": {
"command": "npx",
"args": [
"-y",
"validatehtml",
"mcp"
],
"env": {
"VALIDATEHTML_API_KEY": "your-value"
}
}
}
}Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.
Or copy the settings yourself
Paste into .vscode/mcp.json in your project
{
"servers": {
"validatehtml": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"validatehtml",
"mcp"
],
"env": {
"VALIDATEHTML_API_KEY": "your-value"
}
}
}
}Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.
This one runs on your computer, and ChatGPT can only connect to servers on the internet. Pick another app.
Your choice stays on this device in a cookie; no account needed.
Values you fill in
- Optional. Only audit_page needs it. 100 free calls a month.
These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.
What it can do
Runs on your computer; the tool list appears in your AI app after you install it.
Basic checksi
We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 10, 2026
- ✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account theodcrx, which owns the repo
- … Not checked yet
Still maintained
We have not read this repo from GitHub yet
- … Not checked yet
Has a licence
We have not read this repo from GitHub yet
- – Not applicable
Endpoint responds
This one runs on your computer; there is no internet endpoint
- – Not applicable
Sign-in with OAuth
Runs on your computer and uses local settings instead
- … Not checked yet
No hidden instructions in tool descriptions
Runs on your computer; we can only read tool lists from internet endpoints
Compared with others in Developer toolsi
- More stars than 0% of the other 5724 servers in this category
- Published to the registry more recently than 99% of the other 5724 servers in this category
- Basic checks equal to or better than 100% of the other 5724 servers in this category
Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.
Common questions
Is Validatehtml safe?
It passed 1 of 1 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.
What keys or codes does it need?
You need to fill in: VALIDATEHTML_API_KEY
Does it run on my computer or in the cloud?
It runs on your computer. Your AI app starts it when needed, and data does not pass through the maker’s servers (unless it calls an online service itself).
Is it still maintained?
The GitHub repo last changed –, and the latest version (0.1.0) reached the registry today.
Which apps can use it?
Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. You also need Node.js on your computer.
What can I use instead?
In the same category: REA, Netdata, Front-End Checklist
Alternatives
Servers in the same category from other makers, sorted by stars.
Reading a card:↓ Downloads per weeki★ GitHub starsiThree pillars: reviews · checks · usageiUpdated = latest version published to the registryi
Netdata
Real-time infrastructure monitoring with metrics, logs, alerts, and ML-based anomaly detection.
Runs in the cloud
Front-End Checklist
Review frontend code and live pages against 386 quality-gated web development rules.
Runs in the cloud
README from the maker
Open the README
Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.
validatehtml
Validate HTML, CSS, JSON, XML and accessibility from your terminal or your AI coding agent. Errors are spec violations, warnings are best practices, and modern valid code stays clean.
npx validatehtml index.htmlnpx validatehtml https://example.com npx validatehtml http://localhost:3000 --type accessibility
No account and no key. Exit code 0 when it passes, 1 when it fails, 2 when it could not run, so it fits in a script or a build.
For AI coding agents (MCP)
Claude Code:
claude mcp add validatehtml -- npx -y validatehtml mcpCursor, Windsurf, VS Code and any other MCP client:
{"mcpServers": { "validatehtml": { "command": "npx", "args": ["-y", "validatehtml", "mcp"] } } }
| Tool | What it does | Key |
|---|---|---|
validate_code | Checks HTML, CSS, JSON, XML, or HTML for WCAG issues | No |
validate_file | The same on a local file, without reading it into the conversation | No |
validate_url | Checks a live page, including a dev server on localhost | No |
audit_page | Every check on one deployed page: HTML, accessibility, meta tags, Open Graph, page weight | Yes |
site_scan_link | A link for you to scan a whole site in your browser | No |
Agent skill
skills/validatehtml/SKILL.md tells an agent when to validate and how to read the result (fix errors, report warnings, never claim WCAG compliance). Copy the folder into .claude/skills/ (or your agent's skills folder) next to the MCP server.
Command line
validatehtml <file|url|-> [--type html|css|json|xml|accessibility][--audit] [--fail-on error|warning] [--format text|json] validatehtml mcp
- reads standard input. --audit needs a key.
Key
--audit and audit_page use VALIDATEHTML_API_KEY. Create one at https://validatehtml.com/dashboard. A free account includes 100 calls a month; larger allowances are on the pricing page.
What leaves your machine
The code or file you ask to check is sent to validatehtml.com, checked in memory and not stored. A page on localhost is read on your machine and sent the same way. Only .html, .htm, .css, .json, .xml and .svg files can be read, up to 1 MB. Each call also counts the tool used and the package version, never the content.
Licence
MIT for this client. The licence does not cover the ValidateHTML name.