Slack Notifications From Rails: slack-notifier, slack-ruby-client and Net::HTTP Tested

To send Slack notifications from a Rails app, post JSON to a Slack incoming webhook with Net::HTTP, use the slack-notifier gem for the same thing with less code, or use slack-ruby-client with a bot token when you need the full Web API. On 5 November 2026 we ran all three from Ruby 3.4.12 and Rails 8.1.4.1 in a Docker container against a test workspace, then wired exception_notification so an unhandled error in a Rails route posted itself to Slack. The code below is what we ran, and the output is what we got.

Which one to use

We read each gem's record on rubygems.org on 5 November 2026:

slack-notifier has had no release for over five years, but its job is small and it still worked. For anything beyond posting into one channel, slack-ruby-client is the maintained choice; our slack-ruby-client guide covers it in depth.

Both webhook options need an incoming webhook URL. Our guide to creating a Slack webhook shows the screens. Keep the URL in Rails credentials or an environment variable, never in the repository.

1. Plain Net::HTTP

require "net/http"
require "json"

uri = URI(ENV.fetch("SLACK_WEBHOOK_URL"))
res = Net::HTTP.post(uri, { text: "Deploy finished (Net::HTTP)" }.to_json,
                     "Content-Type" => "application/json")
puts "#{res.code} #{res.body}"

Output: 200 ok. With the last characters of the URL changed, the same script printed 403 invalid_token and raised nothing, so check res.code yourself if a lost alert matters.

2. The slack-notifier gem

require "slack-notifier"

notifier = Slack::Notifier.new(ENV.fetch("SLACK_WEBHOOK_URL"))
res = notifier.ping "Deploy finished (slack-notifier), see [the log](https://example.com/log)"
puts res.map { |r| "#{r.code} #{r.body}" }

Output: 200 ok. The gem rewrote the Markdown link before sending: Slack stored the text as see <https://example.com/log|the log>, Slack's own link format, so "the log" showed as a link. Plain Net::HTTP would have sent the brackets as typed.

3. slack-ruby-client with a bot token

require "slack-ruby-client"

client = Slack::Web::Client.new(token: ENV.fetch("SLACK_BOT_TOKEN"))
msg = client.chat_postMessage(channel: ENV.fetch("SLACK_CHANNEL"), text: "Deploy finished (slack-ruby-client)")
puts "ok=#{msg.ok} ts=#{msg.ts}"

begin
  client.chat_postMessage(channel: "C000BAD", text: "x")
rescue Slack::Web::Api::Errors::SlackError => e
  puts "#{e.class}: #{e.message}"
end

Output:

ok=true ts=1793864307.275429
Slack::Web::Api::Errors::ChannelNotFound: channel_not_found

Unlike the webhook, the client raises on a Slack error, with a class per error code, so a typo in a channel ID cannot fail quietly. It needs a bot token with chat:write, and the bot must be in the channel. The ts it returns lets you reply in a thread or edit the message later, which a webhook cannot do.

Send Rails exceptions to Slack

We made a minimal app with rails new demo --minimal, added two gems and one initializer, and gave it a route that raises:

# Gemfile
gem "exception_notification"
gem "slack-notifier"

# config/initializers/exception_notification.rb
require "exception_notification/rails"
ExceptionNotification.configure do |config|
  config.add_notifier :slack, {
    webhook_url: ENV.fetch("SLACK_WEBHOOK_URL"),
    additional_parameters: { mrkdwn: true }
  }
end

# config/routes.rb
Rails.application.routes.draw do
  get "/boom", to: proc { raise ArgumentError, "invoice total is negative" }
end

We started the server in production mode and requested /boom. The browser got a 500, the log showed ArgumentError (invoice total is negative), and this arrived in Slack along with the three messages above:

The card holds the exception class, the request, the message, the server's hostname and the first backtrace line. Our hostname was the Docker container ID, so the field tells you which server failed only if your hosts have meaningful names. exception_notification uses slack-notifier under the hood for this notifier, which is why both gems are in the Gemfile.

Tips from the run

• • Send from a background job (perform_later) in request code, so a slow Slack response never slows a page. A job also gives you retries.
• • Use one webhook per channel. A webhook made by a Slack app ignores channel, username and icon_emoji overrides; we tested that in our Uptime Kuma Slack guide.
• • For formatting, both webhooks and chat.postMessage read Slack's mrkdwn, not standard Markdown. Our Slack Block Kit Markdown guide shows what renders.

FAQ

Does slack-notifier still work in 2026?

Yes. In our run, version 2.4.0 posted to a current Slack webhook from Ruby 3.4.12 and converted the link as before. It is unmaintained, so for new code that needs more than one-way posts, use slack-ruby-client.

Can Rails 8 send to Slack without a gem?

Yes, with Net::HTTP as in the first example. Rails has no built-in Slack notifier.