Using API

Validating files

import { HtmlValidate } from "html-validate";

const htmlvalidate = new HtmlValidate();
const report = htmlvalidate.validateFile("myfile.html");

console.log("valid", report.valid);
if (!report.valid) {

validateFile is a high-level API which automatically locates configuration files, load plugins, runs any transformations etc and is very similar to using the CLI tool (in fact, the CLI tool uses this very API).

A configuration object may optionally be passed to the HtmlValidate constructor:

const htmlvalidate = new HtmlValidate({
  extends: ["html-validate:recommended"],

If set, it will be used as configuration unless a configuration could be read from .htmlvalidate.json files. Set root: true to prevent configuration files to be searched.

Validating strings and other sources

In addition to validateFile there is also validateString and validateSource. Unlike validateFile no configuration files will be searched from the filesystem and the full configuration must be passed to the HtmlValidate constructor.

const report = htmlvalidate.validateString("<div>lorem ipsum</span>");
const report = htmlvalidate.validateSource({
  /* markup to validate */
  data: "<div>lorem ipsum</span>",

  /* filename to put in report, content is not read */
  filename: "myfile.txt",

  /* original source location, i.e. at what position was markup extracted from
   * in original file. */
  line: 12,
  column: 8,

Handling multiple files

To validate multiple files you need to call validateFile for each one, obtaining a report for each one. The reports can then be merged together, forming a new Report object.

const report1 = htmlvalidate.validateFile("myfile.html");
const report2 = htmlvalidate.validateFile("anotherfile.html");

/* merge reports together to a single report */
const merged = Reporter.merge([report1, report2]);

/* valid is true only if all reports are valid */
console.log("valid", merged.valid);

/* results holds all files */
if (!merged.valid) {

Formatting reports

HTML-validate comes with a number of builtin formatters:

Formatters work on the results property in a report and all returns a formatted string:

import { HtmlValidate } from "html-validate";
import text from "html-validate/dist/formatters/text";

const htmlvalidate = new HtmlValidate();
const report = htmlvalidate.validateFile("myfile.html");


Using the CLI API there is a factory function to retrieve formatters (see html-validate --help for details about the format):

import { getFormatter } from "html-validate/dist/cli/formatter";

const stylish = getFormatter("stylish");

In addition, any ESLint compatible reporter will work:

const stylish = require("eslint/lib/formatters/stylish");

Configuration cache

HtmlValidate is mostly stateless, it only acts on the input source and its configuration.

However, for performance configuration is cached (per instance) and must be flushed if configuration is changed. Normally this wont matter but when writing integrations with tools it might be desirable to keep a single instance of HtmlValidate around and in that case the cache needs to be flushed if configuration changes are detected.

/* flush everything */

/* flush configuration for a single file */

Unit testing

If using jest to write tests there is a couple of helpers to assist writing tests:

import { HtmlValidate } from "html-validate";
import "html-validate/jest";

const config = {
  rules: {
    "my-rule": "error",

test("should frobnicate a tux", () => {
  const htmlvalidate = new HtmlValidate(config);
  const report = htmlvalidate.validateString("...");

test("should not frobnicate a flux", () => {
  const htmlvalidate = new HtmlValidate(config);
  const report = htmlvalidate.validateString("...");
  expect(report).toHaveError("my-rule", "the tux should not be frobnicated by a flux");

CLI tools

The CLI interface can be wrapped using the CLI class.

const cli = new CLI({
  configFile: argv.configFile,
  rules: argv.rules,
const htmlvalidate = cli.getValidator();
const formatter = cli.getFormatter(argv.formatter);
const files = cli.expandFiles("**/*.html");
const report = htmlvalidate.validateMultipleFiles(files);