# validator/validator

The Nu Html Checker (vnu)

Repository: https://github.com/validator/validator
Canonical: https://ross.abutalabs.com/products/validator-validator
Homepage: https://validator.github.io/validator/
Language: Java
License: MIT
License Family: permissive
Topics: linter, web-standards, whatwg, w3c, web-development, devtools, html-linter, html-checker, html-validation
Last push: 2026-08-24T00:01:55+00:00

## Health v2 (maintenance only)
Score: 88/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 67, longevity 100
- inputs: {"age_days": 5753, "days_push": 10, "days_rel": 10, "gap_med": null, "n_releases_24m": 1}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1980, forks 332 (observed 2026-08-28T04:06:01.667935+00:00)

## What it is
The Nu Html Checker (vnu) is the W3C/WHATWG-endorsed tool for validating HTML, CSS, and SVG documents. It runs as a command-line batch checker, a standalone web service, or a servlet-deployable WAR, with pre-compiled binaries, a portable JAR, Docker image, and npm/brew packages.

## Use cases
- validate html files for errors
- check css and svg markup mistakes
- batch-validate a directory of web pages from the command line
- self-host an html validation service like validator.w3.org/nu
- integrate html validation into ci or build tools like grunt or gulp
- lint html in automated scripts

## When to choose
- you need standards-compliant HTML/CSS/SVG validation matching validator.w3.org/nu
- you want to batch-check many files or URLs from the command line
- you want to self-host a validation service via Docker, WAR, or standalone server
- you need cross-platform binaries that don't require Java installed

## When to avoid
- you need linting beyond markup validation, such as JavaScript linting or style enforcement
- you want a browser-based GUI validator without running anything locally
- you need a lightweight pure-JS linter inside a Node build pipeline without Java or binaries

## Facets
- artifact type: cli-tool
- maturity: stable
- function: linter, cli, http-server, developer-tools
- domain: web-development, developer-tools, documentation
- platform: windows, cli, self-hosted, jvm, cross-platform
- tags: html-validation, html-checker, css-validation, svg-validation, w3c, whatwg, web-standards, vnu, java, servlet, npm-package, brew-package, command-line, linux, macos, docker

## Member repositories
- validator/validator (main) score 88

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:01.667935+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T03:04:40.745815+00:00, confidence not recorded.
  - readme: https://github.com/validator/validator (fetched 2026-08-28T04:06:01.667935+00:00, sha 3b7eb2868c27)
  - homepage: https://validator.github.io/validator/ (fetched 2026-08-29T10:43:31.220659+00:00, sha 9778821e3ba8)
- Data as of 2026-08-30T08:39:29.467469+00:00.