// config/plugin.js
exports.validate = {
  enable: true,
  package: 'egg-validate',
};

// config/config.default.js
exports.validate = {
  // convert: false,
  // validateRoot: false,
};

// app/controller/home.js
const Controller = require('egg').Controller;
class HomeController extends Controller {
  async index() {
    const { ctx, app } = this;
    ctx.validate({ id: 'id' }); // will throw if invalid
    // or
    const errors = app.validator.validate({ id: 'id' }, ctx.request.body);
  }
}
module.exports = HomeController;

app.validator.addRule('jsonString', (rule, value) => {
  try {
    JSON.parse(value);
  } catch (err) {
    return 'must be json string';
  }
});