Claude API Ruby Example

Working Ruby code for the Claude API using net/http. No official Ruby gem needed — call Claude from Rails, Sinatra, or plain Ruby scripts with these copy-paste examples.

Anthropic has no official Ruby gem as of 2026, so the idiomatic approach is to call the REST API directly via Ruby's built-in net/http. These examples work in plain Ruby scripts, Rails, and Sinatra.

Minimal example

require 'net/http'
require 'json'
require 'uri'

def claude(prompt, model: "claude-sonnet-4-6", max_tokens: 1024)
  uri = URI("https://api.anthropic.com/v1/messages")
  req = Net::HTTP::Post.new(uri, {
    "x-api-key"         => ENV["ANTHROPIC_API_KEY"],
    "anthropic-version" => "2023-06-01",
    "content-type"      => "application/json"
  })
  req.body = JSON.generate({
    model:      model,
    max_tokens: max_tokens,
    messages:   [{ role: "user", content: prompt }]
  })

  res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
  JSON.parse(res.body).dig("content", 0, "text")
end

puts claude("Explain Ruby blocks in one paragraph.")

With system prompt

req.body = JSON.generate({
  model:      "claude-sonnet-4-6",
  max_tokens: 512,
  system:     "You are a concise Ruby expert. Answer in bullet points.",
  messages:   [{ role: "user", content: "What is the difference between Proc and Lambda?" }]
})

Reusable ClaudeClient class

require 'net/http'
require 'json'
require 'uri'

class ClaudeClient
  BASE_URI = URI("https://api.anthropic.com/v1/messages").freeze

  def initialize(api_key: ENV["ANTHROPIC_API_KEY"], model: "claude-sonnet-4-6")
    @api_key = api_key
    @model   = model
  end

  def chat(messages, system: nil, max_tokens: 1024)
    body = { model: @model, max_tokens: max_tokens, messages: messages }
    body[:system] = system if system

    req = Net::HTTP::Post.new(BASE_URI, headers)
    req.body = JSON.generate(body)

    res = Net::HTTP.start(BASE_URI.hostname, BASE_URI.port, use_ssl: true) { |h| h.request(req) }
    raise "Claude error #{res.code}: #{res.body}" unless res.is_a?(Net::HTTPSuccess)

    JSON.parse(res.body).dig("content", 0, "text")
  end

  private

  def headers
    {
      "x-api-key"         => @api_key,
      "anthropic-version" => "2023-06-01",
      "content-type"      => "application/json"
    }
  end
end

client = ClaudeClient.new
puts client.chat([{ role: "user", content: "Write a Ruby one-liner that reverses each word in a string." }])

Streaming response

require 'net/http'
require 'json'
require 'uri'

uri = URI("https://api.anthropic.com/v1/messages")

Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
  req = Net::HTTP::Post.new(uri, {
    "x-api-key"         => ENV["ANTHROPIC_API_KEY"],
    "anthropic-version" => "2023-06-01",
    "content-type"      => "application/json"
  })
  req.body = JSON.generate({
    model:      "claude-sonnet-4-6",
    max_tokens: 1024,
    stream:     true,
    messages:   [{ role: "user", content: "Explain metaprogramming in Ruby." }]
  })

  http.request(req) do |res|
    buffer = ""
    res.read_body do |chunk|
      buffer += chunk
      while (line = buffer.slice!(/^data: .+
/))
        data = line.sub("data: ", "").strip
        next if data == "[DONE]"
        event = JSON.parse(data) rescue next
        if event.dig("delta", "type") == "text_delta"
          print event.dig("delta", "text")
          $stdout.flush
        end
      end
    end
  end
end
puts

Error handling with retry

def claude_with_retry(prompt, retries: 3)
  delay = 1
  retries.times do |attempt|
    result = claude(prompt)
    return result
  rescue => e
    raise e if attempt == retries - 1
    sleep delay
    delay *= 2
  end
end

Rails integration

# config/initializers/claude.rb
require_relative "../../lib/claude_client"
CLAUDE = ClaudeClient.new(api_key: Rails.application.credentials.anthropic_api_key)

# app/controllers/chat_controller.rb
class ChatController < ApplicationController
  def create
    reply = CLAUDE.chat([{ role: "user", content: params[:message] }])
    render json: { reply: reply }
  end
end

Ruby vs Python SDK comparison

To estimate token costs for your Ruby app, use the Claude API Cost Calculator. For pricing details, see the Anthropic API pricing page.

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