Fix ActionController::UnknownFormat: ActionController::UnknownFormat: TurboStreamController#create is missing a template for this request format and target in Rails

This error occurs when a controller action receives a Turbo Stream request but has no corresponding turbo_stream template or respond_to block handling the format. Create a .turbo_stream.erb template or add format.turbo_stream to your respond_to block to handle Turbo Stream requests properly in your Rails controller.

Reading the Stack Trace

Here's what each line means:

• actionpack (7.1.3) lib/action_controller/metal/implicit_render.rb:43:in `default_render': Rails cannot find a template matching the turbo_stream format for this action.
• app/controllers/comments_controller.rb:10:in `create': The create action does not handle the turbo_stream format explicitly.
• turbo-rails (1.5.0) lib/turbo/broadcastable.rb:130:in `broadcast_action': Turbo Rails is trying to broadcast the result but the format is not handled.

Common Causes

# app/controllers/comments_controller.rb
def create
  @comment = @post.comments.create!(comment_params)
  # No app/views/comments/create.turbo_stream.erb exists
end

def create
  @comment = @post.comments.create!(comment_params)
  redirect_to @post  # Only handles HTML, not turbo_stream
end

<%= form_with model: [@post, Comment.new] do |f| %>
  <%= f.text_area :body %>
  <%= f.submit 'Add Comment' %>
<% end %>
<!-- Turbo submits this as turbo_stream by default -->

The Fix

Add a respond_to block that handles both turbo_stream and HTML formats. Create a .turbo_stream.erb template that uses turbo_stream helpers to update the page. The HTML fallback handles non-Turbo requests.

def create
  @comment = @post.comments.create!(comment_params)
  redirect_to @post
end

def create
  @comment = @post.comments.create!(comment_params)

  respond_to do |format|
    format.turbo_stream
    format.html { redirect_to @post }
  end
end

# app/views/comments/create.turbo_stream.erb
# <%= turbo_stream.append 'comments', partial: 'comments/comment', locals: { comment: @comment } %>

Testing the Fix

require 'rails_helper'

RSpec.describe CommentsController, type: :request do
  let(:post_record) { create(:post) }

  describe 'POST /posts/:post_id/comments' do
    it 'responds to turbo_stream format' do
      post post_comments_path(post_record),
           params: { comment: { body: 'Great post!' } },
           headers: { 'Accept' => 'text/vnd.turbo-stream.html' }
      expect(response).to have_http_status(:ok)
      expect(response.media_type).to eq('text/vnd.turbo-stream.html')
    end

    it 'falls back to HTML redirect' do
      post post_comments_path(post_record),
           params: { comment: { body: 'Great post!' } }
      expect(response).to redirect_to(post_record)
    end
  end
end

Run your tests:

bundle exec rspec spec/requests/comments_spec.rb

Pushing Through CI/CD

git checkout -b fix/rails-turbo-stream-format
git add app/controllers/comments_controller.rb app/views/comments/create.turbo_stream.erb
git commit -m "fix: handle turbo_stream format in comments controller"
git push origin fix/rails-turbo-stream-format

Your CI config should look something like this:

name: CI
on:
  pull_request:
    branches: [main]
jobs:
  test:
    runs-on: ubuntu-latest
    services:
      postgres:
        image: postgres:16
        env:
          POSTGRES_PASSWORD: postgres
        ports: ['5432:5432']
    steps:
      - uses: actions/checkout@v4
      - uses: ruby/setup-ruby@v1
        with:
          ruby-version: '3.3'
          bundler-cache: true
      - run: bin/rails db:setup
      - run: bundle exec rspec

The Full Manual Process: 18 Steps

Here's every step you just went through to fix this one bug:

1. Notice the error alert or see it in your monitoring tool
2. Open the error dashboard and read the stack trace
3. Identify the file and line number from the stack trace
4. Open your IDE and navigate to the file
5. Read the surrounding code to understand context
6. Reproduce the error locally
7. Identify the error source
8. Write the fix
9. Run the test suite locally
10. Fix any failing tests
11. Write new tests covering the edge case
12. Run the full test suite again
13. Create a new git branch
14. Commit and push your changes
15. Open a pull request
16. Wait for code review
17. Merge and deploy to production
18. Monitor production to confirm the error is resolved

Total time: 30-60 minutes. For one bug.

gem install bugstack

require 'bugstack'

Bugstack.init(api_key: ENV['BUGSTACK_API_KEY'])

Deploying the Fix (Manual Path)

1. Create turbo_stream templates for all relevant actions.
2. Add respond_to blocks in controllers.
3. Test with and without Turbo enabled.
4. Open a pull request.
5. Merge and verify Turbo Stream updates work in staging.

Frequently Asked Questions