Localize dates and times in Rails with simple client-side timezone detection

Published on March 31, 2026

When your web browser makes a request to a website, it tells the server which language to serve via the Accept-Language header. Your browser does not tell the web server what time zone to use when serving content, which is key to localizing dates and times.

Rails has excellent support for localizing times via Time.use_zone. Using a bit of JavaScript and a client-side cookie, we can easily solve the inherent localization gap in the browser.

I often use Stimulus with my Rails apps, though the following can be easily adapted to pure JavaScript or to another framework or library.

import { cookie } from 'cookie.js';
import jstz from 'jstimezonedetect';

import { Controller } from '@hotwired/stimulus';

export default class extends Controller {
  connect() {
    this.tz = jstz.determine();
    this.tzName = jstz.determine().name();

    cookie.set('TZ', this.tzName, { path: '/' });
  }
}

Next, we’ll need to consume this cookie server-side and call Time.use_zone via a controller action callback.

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  prepend_around_action :set_timezone

  def set_timezone
    tzone = cookies["TZ"] || "America/New_York"

    Time.use_zone(tzone) { yield }
  end

How easy is that? Now we can easily localize date and time values in views via:

l @user.created_at, format: :short