npm install --save-dev gulp-amphtml-validator

const gulpAmpValidator = require('gulp-amphtml-validator');

gulp.task('amphtml:validate', () => {
  return (
    gulp
      .src('*.html')
      // Validate the input and attach the validation result to the "amp" property
      // of the file object.
      .pipe(gulpAmpValidator.validate())
      // Print the validation results to the console.
      .pipe(gulpAmpValidator.format())
      // Exit the process with error code (1) if an AMP validation error
      // occurred.
      .pipe(gulpAmpValidator.failAfterError())
  );
});

// Exit the process with error code (1) if an AMP validation warning or
// error occurred.
.pipe(gulpAmpValidator.failAfterWarningOrError());