Herb in Rails 8.2: Your ERB views, now HTML-aware @ Rocky Mountain Ruby 2026, Boulder, Colorado

With teams, companies, and open source projects adopting Herb in their daily workflows, the foundation is proving itself at scale and is on track to become an opt-in view engine in Rails 8.2.

This talk explores what Herb brings to Rails: how it integrates with ActionView and the tooling and developer experience every Rails developer gains as a result.

But that's only the beginning. To complete the Hotwire story, Rails needs reactivity.

Herb's understanding of HTML and ERB makes this possible. I'll introduce the first production-ready version of ReActionView, bringing Phoenix LiveView-like fine-grained reactivity to standard Rails templates. Fully optional. Gradual to adopt. No JavaScript framework. No new file format.

Your HTML+ERB templates, now reactive.

Transcript

1. Marco Roth Herb in Rails 8.2: Your ERB views, now HTML-aware Sep 29, 2026 - Rocky Mountain Ruby, Boulder, Colorado
2. 🌐 marcoroth.dev Marco Roth ! Full-Stack Developer & Open Source Contributor  @marcoroth  @marcoroth@ruby.social  @marcoroth_  @marcoroth.dev
4. Developer Tooling & Developer Experience
6. Herb
8. Marco Roth Herb in Rails 8.2: Your ERB views, now HTML-aware Sep 29, 2026 - Rocky Mountain Ruby, Boulder, Colorado
9. What is Herb?
10. What is Herb? What ships in Rails 8.2?
11. What is Herb? What ships in Rails 8.2? What does this enable?
12. What is Herb?
13. A modern templating language for the HTML+ERB you already have.
14. One language and toolchain that understands your HTML and Ruby together.
15. Herb has full semantic and structural understanding of your HTML views.
16. Linter Formatter Language Server Engine Dev Tools Dev Server
20. herb dev
23. Herb helps you in development, in your editor, in CI, and when rendering your views.
24. What ships in Rails 8.2?
25. Action View
26. Herb? Action View
27. index.html.erb
28. index.html.erb action
29. index.html.erb action format
30. index.html.erb action format handler
31. Herb is the new default for the HTML format
32. format == :html && handler == :erb
33. *.html.erb → Herb
34. *.html.erb → Herb *.****.erb → Erubi
35. bin/rails herb:check
36. config.action_view .erb_implementation=
37. config/application.rb config.load_defaults 8.2
38. Rails 8.2 defaults .erb_implementation = :herb
39. Restore previous behavior .erb_implementation = :erubi
41. LSP features
42. Find all references Workspaces Support Hover Previews Extract to Partial Cross File Diagnostics
43. Runtime Instrumentation
44. ActiveSupport::Notifications .subscribe("sql.active_record") do |*, payload| Herb::Engine::Report::Session.observe( :queries, payload ) end
45. Runtime Diagnostics
49. LSP Runtime Inlay Hints
53. 68 new linter rules
55. 166 linter rules
58. https://herb-tools.dev/blog/whats-new-in-herb-v0-11
59. What does this enable?
60. The Herb foundation is available in all new apps
61. The Compiler as a Platform
62. One-Person Framework
63. Rails 7 brought a lot of simplification with Hotwire
64. HTML-over-the-wire
65. Rails 8 brought a lot of simplification with the Solid Trifecta
66. The View Layer in Rails doesn't scale the same way as the rest of the framework does.
67. What becomes possible when the engine and runtime also understand HTML?
68. How can we evolve Hotwire so you can build competitive, modern, and ambitious UIs?
69. What does it take to complete the Hotwire story?
70. Reactivity
71. Fine-grained reactivity
72. The design goal for Herb tooling was to be fully backwards compatible for existing HTML+ERB files
73. I was curious if we can do the same for templating, reactivity, and interactivity.
74. I wanted to explore if there is a way how I can revisit some of the old and untapped ideas from StimulusReflex
77. ActionView
78. ActionView Reimagined
79. ActionView Reimagined Reengineered
80. ActionView Reimagined Reengineered Reactive
83. ReActionView v0.6
84. Reactivity for the HTML+ERB you already have.
85. Everything a clientside framework gives you, without adopting one.
86. And the best thing?
87. You already wrote a ReActionView template.
88. Your existing HTML+ERB views are now reactive.
89. 6 Adoption Levels of ReActionView
90. Level 1 - Better Errors Messages Level 2 - HTML-aware Engine Level 3 - Action View Optimizations Level 4 - Reactive ERB Views Level 5 - Client-side Templates Level 6 - External Components
91. Slots
92. <section> <h2><%= @title %></h2> <ul> <% @albums.each do |album| %> <li id="<%= album.id %>"> <%= album.name %> </li> <% end %> </ul> </section>
93. <section> <h2><%= @title %></h2> <ul> <% @albums.each do |album| %> <li id="<%= album.id %>"> <%= album.name %> </li> <% end %> </ul> </section>
94. <section> <h2><%= @title %></h2> <ul> <% @albums.each do |album| %> <li id="<%= album.id %>"> <%= album.name %> </li> <% end %> </ul> </section>
95. <section> <h2><%= @title %></h2> <ul> <% @albums.each do |album| %> <li id="<%= album.id %>"> <%= album.name %> </li> <% end %> </ul> </section>
96. Herb fully understands what the view is doing
97. So we can compile the template into two formats to support reactivity.
98. One for the regular render, and one for this new slots format
99. <h2>Hello, <%= @title %>!</h2>
100. <h2>Hello, RMR!</h2>
101. <h2>Hello, RMR!</h2>
102. <h2> Hello, <!--herb-slot:1-->RMR<!--/herb-slot:1-->! </h2>
103. <h2> Hello, <!--herb-slot:1-->RMR<!--/herb-slot:1-->! </h2>
104. <!--herb-region:test.html.erb--> <h2> Hello, <!--herb-slot:1-->RMR<!--/herb-slot:1-->! </h2> <!--/herb-region:test.html.erb-->
105. <!--herb-region:test.html.erb--> <h2> Hello, <!--herb-slot:1-->Boulder<!--/herb-slot:1-->! </h2> <!--/herb-region:test.html.erb-->
106. Both the server and the client have a map of where the dynamic slot values go
107. Wherever new values come from, the client knows how to update it.
108. ERB Output Collections/Loops Conditionals
109. No page reloads. No DOM-morphing.
110. <div class="container"> <%= Time.now %> </div>
111. <div class="container"> <%= Time.now %> <button data-herb-action="$refresh">Refresh</button> </div>
112. <div class="container"> <%= Time.now %> <button data-herb-action="$refresh">Refresh</button> </div>
113. GET /demo Accept: application/vnd.herb.slots+json
114. def show end
115. def show respond_to do |format| format.html end end
116. def show respond_to do |format| format.html format.slots end end
117. GET /demo Accept: application/vnd.herb.slots+json { "template": "app/views/demo/show.html.erb", "version": "ddfca612", "occurrence": 0, "slots": { "0": "2026-09-24 12:14:38 +0200" } }
118. GET /demo Accept: application/vnd.herb.slots+json { "template": "app/views/demo/show.html.erb", "version": "ddfca612", "occurrence": 0, "slots": { "0": "2026-09-24 12:14:38 +0200" } }
119. State
120. Not every UI interaction should require a serverroundtrip
121. Typically you would reach for Stimulus
122. But, what if you could just write this in ERB?
123. <button>Show Details</button> <% if show? %> <span>Here are the details!</span> <% end %>
124. <%# herb:state (show: false) %> <button>Show Details</button> <% if show? %> <span>Here are the details!</span> <% end %>
125. <%# herb:state (show: false) %> <button data-herb-set="click->show=true">Show Details</button> <% if show? %> <span>Here are the details!</span> <% end %>
126. <%# herb:state (show: false) %> <button data-herb-set="show=true">Show Details</button> <% if show? %> <span>Here are the details!</span> <% end %>
127. <%# herb:state (show: false) %> <button data-herb-set="show=true">Show Details</button> <% if show? %> <span>Here are the details!</span> <% end %>
128. <%# herb:state (show: false) %> <button data-herb-toggle="show">Show Details</button> <% if show? %> <span>Here are the details!</span> <% end %>
129. data-herb-set data-herb-action data-herb-toggle data-herb-increment data-herb-decrement
130. Two-way bindings
131. <input value="<%= message %>">
132. <%# herb:state (message: "") %> <input value="<%= message %>">
133. You now got a twoway binding
134. <%# herb:state (message: "") %> <input value="<%= message %>"> <p><%= message.length %> characters</p>
135. No network request needed
136. No custom JavaScript needed
137. Just pure understanding and efficient updates
138. No Ruby to JavaScript transpilation
139. So we don't need to run Ruby in WebAssembly in the browser
140. ReActionView sees all the methods that are being called on a herb:state local variable
141. The compiler understands a subset of Ruby that it can wire into the reactivity model
142. That way, it can run fully client-side without a server round-trip
143. For everything the compiler doesn't support, we do a network request
144. <%# herb:state (q: "") %> <input value="<%= q %>"> <% if q.present? %> <p><%= Topic.search(q).count %> results</p> <% end %>
145. The compiler prepares the view in a way so the client knows on which state change it has to rerequest the data
146. When the client has to request it, the server knows how to respond
147. and the client knows how to update and insert the new dynamic slot values
148. No Turbo Frames No Turbo Streams No new route
149. Just pure understanding of the view and finegrained reactivity.
150. Lazy Loading
151. <p><%= Stats.slow_query %></p>
152. <Async> <p><%= Stats.slow_query %></p> </Async>
153. <Async> <p><%= Stats.slow_query %></p> <Fallback> <p class="skeleton">&nbsp;</p> </Fallback> </Async>
154. <Lazy> <p><%= Stats.slow_query %></p> <Fallback> <p class="skeleton">&nbsp;</p> </Fallback> </Lazy>
156. Open to feedback about naming
158. Optimistic UI
160. You can do a lot with pure ERB
161. If you need to, there is a JavaScript API you can use to interact with the client runtime directly
162. Which also allows to build even more ambitious UIs, or allows to wire up NPM packages
163. bundle add reactionview rails generate reactionview:install
164. reactionview.dev demo.reactionview.dev
165. Outlook/Vision
166. <style scoped>
167. lightningcss-ruby
168. <script scoped>
169. oxc-ruby
170. rolldown-ruby
171. Offline Mode React Components Herb Components for gems Client-side routing
172. Conclusion
173. I'm really happy with the direction Herb and ReActionView are taking and how they are shaping up
174. And, how we can go back to just keep writing ERB views and get fully reactive UIs
175. I believe that this offers a great foundation for the future of the Rails frontend
176. The idea is to offer a spectrum for teams to adopt
177. Expand what's possible with Hotwire today
178. Allow people to write more JavaScript if the application needs it
179. And in case you'd want to use React or existing components, that you still have a way to use them alongside your ERB views
180. Without having to abandon the full-stack approach that makes Rails so special
182. ReActionView has become what I always wanted StimulusReflex to be
183. But I'm sure there are more things we can do, improve, and iterate on.
184. But I can't do it all by myself, I need your input.
185. I would love to talk to you if you have ideas or opinions about the things I have shown today.
186. Or if you are still skeptical and have questions on where things are heading
187. I would love your input and feedback
188. Acknowledgments
191.  github.com/sponsors/marcoroth
192. Thank you for the continued support!
193. Please try the tools, report issues, and give feedback.
196. herb-tools.dev reactionview.dev
199. Thank you "  @marcoroth 🌐 marcoroth.dev  @marcoroth_  @marcoroth.dev  @marcoroth@ruby.social  /in/marco-roth