Ships with Rails 8.2

A modern templating language for the HTML+ERB you already have.

One language and toolchain that understands your HTML and Ruby together.

Lint · Format · Analyze · Render · Tooling

Get started Try it in the browser Language reference

herb-lint app/views/users/show.html.erb

[warning] Prefer `image_tag` helper over manual `<img>` with dynamic ERB expressions. (erb-prefer-image-tag-helper)

app/views/users/show.html.erb:2:7

      1 │ <div class="avatar">
  →   2 │   <img src="<%= user.avatar_url %>">
        │        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      3 │ </div>

[1/2]

[warning] Missing required `alt` attribute on `<img>` tag. (html-img-require-alt)

 Summary:
  Checked      1 file
  Offenses     2 warnings
  Rules        146 enabled | 22 not enabled
  Duration     34ms

Your HTML+ERB, upgraded.

The same files you have now, understood properly for the first time.

Catch mistakes before they ship

168 rules covering accessibility, HTML correctness, Action View usage and security, with 146 on by default. Run them in your editor, on commit, or in CI.

$ herb-lint

 Rule offenses:
  a11y-avoid-generic-link-text (14 offenses in 9 files)
  actionview-no-implicit-partial (6 offenses in 4 files)
  html-img-require-alt (3 offenses in 3 files)

 Summary:
  Checked      144 files
  Offenses     23 warnings
  Fixable      9 offenses

Format templates automatically

Indentation, line wrapping and attribute layout that respect both the HTML tree and the ERB inside it. Nothing gets reflowed into the wrong branch.

before
<div  class="card"   id="u"><%= u.name %></div>

after
<div class="card" id="u">
  <%= u.name %>
</div>

Understand templates in your editor

Hover, go to definition, diagnostics and code actions for HTML+ERB. Works in VS Code, Zed, Neovim and anything else that speaks LSP.

<%= render "users/card", user: user %>
             └─ app/views/users/_card.html.erb

             strict locals:
               user:     required
               compact:  = false

You already know Herb.

app/views/users/show.html.erb

<h1>Hello, <%= @user.name %></h1>

<% if @user.admin? %>
  <span class="badge">Admin</span>
<% end %>

That is Herb. Your existing .html.erb templates are already valid Herb templates, so there is nothing to rename and no new syntax to learn.

There is nothing to learn.
You already know Herb.

Your editor and your server see the same template.

Everything below is built on the same parser, so the linter, the formatter, your editor and the renderer all share one foundation.

Working with HTML+ERB

Development and CI

Linter
Formatter experimental
Language Server
Dev Server experimental
Dev Tools

Rendering HTML+ERB

Production runtime

Building on Herb

Wherever you call them

You may already have it.

Herb ships inside tools you already use, so there is a good chance you are already running it without having it installed explicitly.

Rails 8.2

Herb::Engine is the default for HTML-format templates. Your .html.erb views render through Herb with nothing configured, and other formats such as .json.erb fall back to Erubi.

Tilt 2.9.0

Ships a Herb template registered for .herb and .html.erb. Tilt is the template interface behind Sinatra, Roda and Hanami's view layer, so Herb is available there with no wiring of your own.

Zed

The Herb Language Server comes pre-installed with Zed's official Ruby extension. Install the Ruby extension and it is there.

Supercharging Herb with ReActionView

Want to take your templates further and build dynamic interfaces without a JavaScript framework? ReActionView makes your existing HTML+ERB templates reactive, with fine-grained updates down to a single value, attribute or row, and no new syntax or build step.

Explore ReActionView →

Supported by 36 people and companies.

Herb is an independent open source project, and it relies on the companies that use it to keep going. If your team depends on Herb, consider sponsoring the project.

Grant 2026 Gem Fellow. Herb was one of eight projects selected for the 2026 Gem Fellowship, a grant partnership between gem.coop and Contributed Systems, the company behind Sidekiq. It funded stabilization work toward 1.0 and the groundwork for reactive rendering. Read the final report →

Run it on the templates you have.

Nothing to add to your Gemfile. This parses every template in the project and reports what it finds.

$ gem exec herb analyze

Installation Language reference GitHub