ERB review

Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

ERB is a template processor included in Ruby’s standard library. It takes plain-text templates with Ruby expression tags, executable code, and comments, then evaluates the resulting Ruby code to produce a string. That makes it a fit for Ruby developers who want to generate text from templates within Ruby applications or scripts, including plain text and HTML. It is a developer library, not a hosted service.

The central capability is embedding Ruby directly in a template. A supplied binding lets a template access local variables and constants, while templates can also define methods, modules, and classes. This gives ERB a code-generation syntax model and room for logic beyond simple value insertion. It also means ERB is best suited to teams already comfortable placing executable Ruby in templates; developers seeking a language-neutral or strictly declarative template format should consider a different engine.

ERB is free and open source, and is distributed under Ruby’s free-software licensing terms. It is self-hosted as part of the Ruby development environment rather than offered as a hosted service. Encoding controls and configurable whitespace trimming address output-formatting needs, but ERB’s focus remains Ruby template processing. Choose it when Ruby integration and direct access to Ruby values matter more than a broad cross-language feature set; look elsewhere if the project needs a hosted workflow or templates independent of Ruby.

ERB pros and cons

• Where it wins
  • Processes Ruby expressions, executable code, and comment tags in templates
  • Bindings expose local variables and constants to templates
  • Supports encoding settings and configurable whitespace trimming
• Where it doesn't
  • Focused on Ruby rather than templates for other programming languages
  • Templates can execute Ruby code, so they are not just declarative markup
  • A developer library, not a hosted template service

ERB fact sheet, pricing and score →

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Last updated 29 Oct 2026 · How we research and update