Promptly

Opinionated Rails integration for reusable AI prompt templates. Build maintainable, localized, and testable AI prompts using ERB or Liquid templates with Rails conventions.

• Template rendering: ERB (via ActionView) and optional Liquid support
• I18n integration: Automatic locale fallback (welcome.es.erb → welcome.en.erb → welcome.erb)
• Rails conventions: Store prompts in app/prompts/ with organized subdirectories
• Render & CLI: Test prompts in Rails console or via rake tasks
• Minimal setup: Auto-loads via Railtie, zero configuration required
• Prompt caching: Configurable cache store, TTL, and cache-bypass options
• Schema Validation: Ensure all locals passed to templates match a defined schema.

For detailed documentation, please visit the Promptly Wiki.

Add to your Gemfile:

gem "promptly"

For Liquid template support, also add:

gem "liquid"

Then run:

bundle install

# In a controller, service, or anywhere in Rails
prompt = Promptly.render(
  "user_onboarding/welcome_email",
  locale: :es,
  locals: {
    name: "María García",
    app_name: "ProjectHub",
    user_role: "Team Lead",
    features: ["Create projects", "Invite team members", "Track progress", "Generate reports"],
    days_since_signup: 2
  }
)

# Send to your AI service (OpenAI, Anthropic, etc.)
ai_response = openai_client.completions(
  model: "gpt-4",
  messages: [{role: "user", content: prompt}]
)

puts ai_response.dig("choices", 0, "message", "content")
# => AI-generated personalized welcome email in Spanish

Promptly supports OpenAI's structured outputs (guided_json style) by defining .response.json files alongside your templates.

For example, given an output schema app/prompts/user_onboarding/welcome.response.json, you can pass it directly to an AI service:

# Returns the schema wrapped in expected OpenAI format
response_format = Promptly.response_format("user_onboarding/welcome", strict: true)

ai_response = openai_client.chat(
  parameters: {
    model: "gpt-4o",
    messages: [{role: "user", content: prompt}],
    response_format: response_format
  }
)

You can also natively validate the returned JSON string in Ruby to ensure it conforms exactly to the schema:

raw_json = ai_response.dig("choices", 0, "message", "content")

begin
  # Validates and parses the JSON, or raises Promptly::ValidationError
  parsed_output = Promptly.validate_response!("user_onboarding/welcome", raw_json)
rescue Promptly::ValidationError => e
  # Handle invalid response
end

# Install dependencies
bundle install

# Run tests
bundle exec rspec

# Run linter
bundle exec standardrb

# Build gem
rake build

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

MIT