diff --git a/.github/workflows/lint-js-and-ruby.yml b/.github/workflows/lint-js-and-ruby.yml
index a4138195ac..6cdc9900ec 100644
--- a/.github/workflows/lint-js-and-ruby.yml
+++ b/.github/workflows/lint-js-and-ruby.yml
@@ -89,8 +89,12 @@ jobs:
         run: bundle check --path=vendor/bundle || bundle _2.5.9_ install --path=vendor/bundle --jobs=4 --retry=3
       - name: Lint Ruby
         run: bundle exec rubocop
-      - name: Install Node modules with Yarn for dummy app
-        run: cd spec/dummy && yarn install --no-progress --no-emoji --frozen-lockfile
+      - name: Validate RBS type signatures
+        run: bundle exec rake rbs:validate
+      # TODO: Re-enable Steep once RBS signatures are complete for all checked files
+      # Currently disabled because 374 type errors need to be fixed first
+      # - name: Run Steep type checker
+      #   run: bundle exec rake rbs:steep
       - name: Save dummy app ruby gems to cache
         uses: actions/cache@v4
         with:
diff --git a/.github/workflows/pro-lint.yml b/.github/workflows/pro-lint.yml
index 41b10e2f21..4b75353562 100644
--- a/.github/workflows/pro-lint.yml
+++ b/.github/workflows/pro-lint.yml
@@ -141,6 +141,9 @@ jobs:
       - name: Lint Ruby
         run: bundle exec rubocop
 
+      - name: Validate RBS type signatures
+        run: bundle exec rake rbs:validate
+
       - name: Lint JS
         run: yarn run nps eslint
 
diff --git a/.rubocop.yml b/.rubocop.yml
index 0c1270fd09..2a16e98455 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -39,6 +39,7 @@ Naming/FileName:
   Exclude:
     - '**/Gemfile'
     - '**/Rakefile'
+    - '**/Steepfile'
 
 Layout/LineLength:
   Max: 120
diff --git a/CLAUDE.md b/CLAUDE.md
index fa18a77374..09e37b0761 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -45,6 +45,11 @@ Pre-commit hooks automatically run:
   - Check formatting without fixing: `yarn start format.listDifferent`
 - **Build**: `yarn run build` (compiles TypeScript to JavaScript in packages/react-on-rails/lib)
 - **Type checking**: `yarn run type-check`
+- **RBS Type Checking**:
+  - Validate RBS signatures: `bundle exec rake rbs:validate`
+  - Run Steep type checker: `bundle exec rake rbs:steep`
+  - Run both: `bundle exec rake rbs:all`
+  - List RBS files: `bundle exec rake rbs:list`
 - **⚠️ MANDATORY BEFORE GIT PUSH**: `bundle exec rubocop` and fix ALL violations + ensure trailing newlines
 - Never run `npm` commands, only equivalent Yarn Classic ones
 
@@ -117,6 +122,60 @@ This script:
 - 🔄 **Deduplicates** - removes duplicate specs
 - 📁 **Auto-detects directory** - runs from spec/dummy when needed
 
+## RBS Type Checking
+
+React on Rails uses RBS (Ruby Signature) for static type checking with Steep.
+
+### Quick Start
+
+- **Validate signatures**: `bundle exec rake rbs:validate` (run by CI)
+- **Run type checker**: `bundle exec rake rbs:steep` (currently disabled in CI due to existing errors)
+- **Runtime checking**: Enabled by default in tests when `rbs` gem is available
+
+### Runtime Type Checking
+
+Runtime type checking is **ENABLED BY DEFAULT** during test runs for:
+- `rake run_rspec:gem` - Unit tests
+- `rake run_rspec:dummy` - Integration tests
+- `rake run_rspec:dummy_no_turbolinks` - Integration tests without Turbolinks
+
+**Performance Impact**: Runtime type checking adds overhead (typically 5-15%) to test execution. This is acceptable during development and CI as it catches type errors in actual execution paths that static analysis might miss.
+
+To disable runtime checking (e.g., for faster test iterations during development):
+```bash
+DISABLE_RBS_RUNTIME_CHECKING=true rake run_rspec:gem
+```
+
+**When to disable**: Consider disabling during rapid test-driven development cycles where you're running tests frequently. Re-enable before committing to catch type violations.
+
+### Adding Type Signatures
+
+When creating new Ruby files in `lib/react_on_rails/`:
+
+1. **Create RBS signature**: Add `sig/react_on_rails/filename.rbs`
+2. **Add to Steepfile**: Include `check "lib/react_on_rails/filename.rb"` in Steepfile
+3. **Validate**: Run `bundle exec rake rbs:validate`
+4. **Type check**: Run `bundle exec rake rbs:steep`
+5. **Fix errors**: Address any type errors before committing
+
+### Files Currently Type-Checked
+
+See `Steepfile` for the complete list. Core files include:
+- `lib/react_on_rails.rb`
+- `lib/react_on_rails/configuration.rb`
+- `lib/react_on_rails/helper.rb`
+- `lib/react_on_rails/packer_utils.rb`
+- `lib/react_on_rails/server_rendering_pool.rb`
+- And 5 more (see Steepfile for full list)
+
+### Pro Package Type Checking
+
+The Pro package has its own RBS signatures in `react_on_rails_pro/sig/`.
+
+Validate Pro signatures:
+```bash
+cd react_on_rails_pro && bundle exec rake rbs:validate
+```
 ## Changelog
 
 - **Update CHANGELOG.md for user-visible changes only** (features, bug fixes, breaking changes, deprecations, performance improvements)
diff --git a/Gemfile.development_dependencies b/Gemfile.development_dependencies
index 918ce9f488..dd89e56930 100644
--- a/Gemfile.development_dependencies
+++ b/Gemfile.development_dependencies
@@ -34,6 +34,7 @@ group :development, :test do
   gem "pry-rails"
   gem "pry-rescue"
   gem "rbs", require: false
+  gem "steep", require: false
   gem "rubocop", "1.61.0", require: false
   gem "rubocop-performance", "~>1.20.0", require: false
   gem "rubocop-rspec", "~>2.26", require: false
diff --git a/Gemfile.lock b/Gemfile.lock
index 5524b4388c..6c6cf6dec0 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -120,7 +120,8 @@ GEM
       thor (>= 0.19.4, < 2.0)
       tins (~> 1.6)
     crass (1.0.6)
-    cypress-on-rails (1.19.0)
+    csv (3.3.5)
+    cypress-on-rails (1.20.0)
       rack
     date (3.3.4)
     debug (1.9.2)
@@ -135,6 +136,7 @@ GEM
     erubi (1.13.1)
     execjs (2.9.1)
     ffi (1.16.3)
+    fileutils (1.8.0)
     gem-release (2.2.2)
     generator_spec (0.10.0)
       activesupport (>= 3.0.0)
@@ -349,6 +351,7 @@ GEM
       sass (~> 3.5, >= 3.5.5)
     sdoc (2.6.1)
       rdoc (>= 5.0)
+    securerandom (0.4.1)
     selenium-webdriver (4.9.0)
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2, < 3.0)
@@ -375,11 +378,29 @@ GEM
       sprockets (>= 3.0.0)
     sqlite3 (1.7.3)
       mini_portile2 (~> 2.8.0)
+    steep (1.9.4)
+      activesupport (>= 5.1)
+      concurrent-ruby (>= 1.1.10)
+      csv (>= 3.0.9)
+      fileutils (>= 1.1.0)
+      json (>= 2.1.0)
+      language_server-protocol (>= 3.15, < 4.0)
+      listen (~> 3.0)
+      logger (>= 1.3.0)
+      parser (>= 3.1)
+      rainbow (>= 2.2.2, < 4.0)
+      rbs (~> 3.8)
+      securerandom (>= 0.1)
+      strscan (>= 1.0.0)
+      terminal-table (>= 2, < 4)
+      uri (>= 0.12.0)
     stringio (3.1.7)
     strscan (3.1.0)
     sync (0.5.0)
     term-ansicolor (1.8.0)
       tins (~> 1.0)
+    terminal-table (3.0.2)
+      unicode-display_width (>= 1.1.1, < 3)
     thor (1.4.0)
     tilt (2.3.0)
     timeout (0.4.1)
@@ -399,6 +420,7 @@ GEM
     uglifier (4.2.0)
       execjs (>= 0.3.0, < 3)
     unicode-display_width (2.5.0)
+    uri (1.1.1)
     webdrivers (5.3.0)
       nokogiri (~> 1.6)
       rubyzip (>= 1.3.0)
@@ -458,6 +480,7 @@ DEPENDENCIES
   spring (~> 4.0)
   sprockets (~> 4.0)
   sqlite3 (~> 1.6)
+  steep
   turbo-rails
   turbolinks
   uglifier
diff --git a/Steepfile b/Steepfile
new file mode 100644
index 0000000000..bc0d583f43
--- /dev/null
+++ b/Steepfile
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+# Steepfile - Configuration for Steep type checker
+# See https://github.com/soutaro/steep for documentation
+#
+# IMPORTANT: This file lists only the files that are ready for type checking.
+# We use a positive list (explicit check statements) rather than checking all files
+# because not all files have RBS signatures yet.
+#
+# Files/directories intentionally excluded (no RBS signatures yet):
+# - lib/generators/**/*           - Rails generators (complex Rails integration)
+# - lib/react_on_rails/engine.rb  - Rails engine setup
+# - lib/react_on_rails/doctor.rb  - Diagnostic tool
+# - lib/react_on_rails/locales/**/* - I18n files
+# - lib/react_on_rails/props_js_builder.rb - TODO: Add signature
+# - lib/react_on_rails/shakapacker/**/* - Shakapacker integration (complex)
+#
+# To add a new file to type checking:
+# 1. Create corresponding RBS signature in sig/react_on_rails/filename.rbs
+# 2. Add `check "lib/react_on_rails/filename.rb"` below
+# 3. Run `bundle exec rake rbs:steep` to verify
+# 4. Fix any type errors before committing
+
+D = Steep::Diagnostic
+
+target :lib do
+  # Core files with RBS signatures (alphabetically ordered for easy maintenance)
+  check "lib/react_on_rails.rb"
+  check "lib/react_on_rails/configuration.rb"
+  check "lib/react_on_rails/controller.rb"
+  check "lib/react_on_rails/git_utils.rb"
+  check "lib/react_on_rails/helper.rb"
+  check "lib/react_on_rails/packer_utils.rb"
+  check "lib/react_on_rails/server_rendering_pool.rb"
+  check "lib/react_on_rails/test_helper.rb"
+  check "lib/react_on_rails/utils.rb"
+  check "lib/react_on_rails/version_checker.rb"
+
+  # Specify RBS signature directories
+  signature "sig"
+
+  # Configure libraries (gems) - Steep will load their RBS signatures
+  configure_code_diagnostics(D::Ruby.default)
+
+  # Library configuration - standard library gems used by checked files
+  library "pathname"
+  library "singleton"
+  library "logger"
+  library "monitor"
+  library "securerandom"
+end
diff --git a/rakelib/rbs.rake b/rakelib/rbs.rake
index bd4a754a8b..efc80488ad 100644
--- a/rakelib/rbs.rake
+++ b/rakelib/rbs.rake
@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+require "open3"
+require "timeout"
+
 # rubocop:disable Metrics/BlockLength
 namespace :rbs do
   desc "Validate RBS type signatures"
@@ -9,17 +12,21 @@ namespace :rbs do
 
     puts "Validating RBS type signatures..."
 
-    # Run RBS validate
-    result = system("bundle exec rbs -I sig validate")
+    # Use Open3 for better error handling - captures stdout, stderr, and exit status separately
+    # This allows us to distinguish between actual validation errors and warnings
+    # Note: Must use bundle exec even though rake runs in bundle context because
+    # spawned shell commands via Open3.capture3() do NOT inherit bundle context
+    # Wrap in Timeout to prevent hung processes in CI environments (60 second timeout)
+    stdout, stderr, status = Timeout.timeout(60) do
+      Open3.capture3("bundle exec rbs -I sig validate")
+    end
 
-    case result
-    when true
+    if status.success?
       puts "✓ RBS validation passed"
-    when false
+    else
       puts "✗ RBS validation failed"
-      exit 1
-    when nil
-      puts "✗ RBS command not found or could not be executed"
+      puts stdout unless stdout.empty?
+      warn stderr unless stderr.empty?
       exit 1
     end
   end
@@ -34,5 +41,30 @@ namespace :rbs do
     sig_files.each { |f| puts "  #{f}" }
     puts "\nTotal: #{sig_files.count} files"
   end
+
+  desc "Run Steep type checker"
+  task :steep do
+    puts "Running Steep type checker..."
+
+    # Use Open3 for better error handling
+    # Note: Must use bundle exec even though rake runs in bundle context because
+    # spawned shell commands via Open3.capture3() do NOT inherit bundle context
+    # Wrap in Timeout to prevent hung processes in CI environments (60 second timeout)
+    stdout, stderr, status = Timeout.timeout(60) do
+      Open3.capture3("bundle exec steep check")
+    end
+
+    if status.success?
+      puts "✓ Steep type checking passed"
+    else
+      puts "✗ Steep type checking failed"
+      puts stdout unless stdout.empty?
+      warn stderr unless stderr.empty?
+      exit 1
+    end
+  end
+
+  desc "Run all RBS checks (validate + steep)"
+  task all: %i[validate steep]
 end
 # rubocop:enable Metrics/BlockLength
diff --git a/rakelib/run_rspec.rake b/rakelib/run_rspec.rake
index 5fe467ec25..2e27bbcff5 100644
--- a/rakelib/run_rspec.rake
+++ b/rakelib/run_rspec.rake
@@ -20,20 +20,59 @@ namespace :run_rspec do
 
   spec_dummy_dir = File.join("spec", "dummy")
 
+  # RBS Runtime Type Checking Configuration
+  # ========================================
+  # Runtime type checking is ENABLED BY DEFAULT when RBS gem is available
+  # Use ENV["DISABLE_RBS_RUNTIME_CHECKING"] = "true" to disable
+  #
+  # Coverage Strategy:
+  # - :gem task - Enables checking for ReactOnRails::* (direct gem unit tests)
+  # - :dummy tasks - Enables checking (integration tests exercise gem code paths)
+  # - :example tasks - No checking (examples are user-facing demo apps)
+  #
+  # Rationale per Evil Martians best practices:
+  # Runtime checking catches type errors in actual execution paths that static
+  # analysis might miss. Dummy/integration tests exercise more code paths than
+  # unit tests alone, providing comprehensive type safety validation.
+  def rbs_runtime_env_vars
+    return "" if ENV["DISABLE_RBS_RUNTIME_CHECKING"] == "true"
+
+    begin
+      require "rbs"
+      # Preserve existing RUBYOPT flags (e.g., --enable-yjit, --jit, warnings toggles)
+      # by appending RBS runtime hook instead of replacing
+      existing_rubyopt = ENV.fetch("RUBYOPT", nil)
+      rubyopt_parts = ["-rrbs/test/setup", existing_rubyopt].compact.reject(&:empty?)
+      "RBS_TEST_TARGET='ReactOnRails::*' RUBYOPT='#{rubyopt_parts.join(' ')}'"
+    rescue LoadError
+      # RBS not available - silently skip runtime checking
+      # This is expected in environments without the rbs gem
+      ""
+    end
+  end
+
   desc "Run RSpec for top level only"
   task :gem do
-    run_tests_in("", rspec_args: File.join("spec", "react_on_rails"))
+    run_tests_in("",
+                 rspec_args: File.join("spec", "react_on_rails"),
+                 env_vars: rbs_runtime_env_vars)
   end
 
   desc "Runs dummy rspec with turbolinks"
   task dummy: ["dummy_apps:dummy_app"] do
-    run_tests_in(spec_dummy_dir)
+    run_tests_in(spec_dummy_dir,
+                 env_vars: rbs_runtime_env_vars)
   end
 
   desc "Runs dummy rspec without turbolinks"
   task dummy_no_turbolinks: ["dummy_apps:dummy_app"] do
+    # Build env vars array for robustness with complex environment variables
+    env_vars_array = []
+    env_vars_array << rbs_runtime_env_vars unless rbs_runtime_env_vars.empty?
+    env_vars_array << "DISABLE_TURBOLINKS=TRUE"
+    env_vars = env_vars_array.join(" ")
     run_tests_in(spec_dummy_dir,
-                 env_vars: "DISABLE_TURBOLINKS=TRUE",
+                 env_vars: env_vars,
                  command_name: "dummy_no_turbolinks")
   end
 
diff --git a/react_on_rails_pro/Gemfile.development_dependencies b/react_on_rails_pro/Gemfile.development_dependencies
index 92c9ead62b..926c07ec3a 100644
--- a/react_on_rails_pro/Gemfile.development_dependencies
+++ b/react_on_rails_pro/Gemfile.development_dependencies
@@ -50,6 +50,7 @@ group :development, :test do
   gem 'pry-rails' # Causes rails console to open pry. `DISABLE_PRY_RAILS=1 rails c` can still open with IRB
   gem 'pry-theme' # An easy way to customize Pry colors via theme files
 
+  gem "rbs", require: false
   gem "rubocop", "1.36.0", require: false
   gem 'rubocop-performance', "1.15.0", require: false
   gem 'rubocop-rspec', "2.13.2", require: false
diff --git a/react_on_rails_pro/rakelib/rbs.rake b/react_on_rails_pro/rakelib/rbs.rake
new file mode 100644
index 0000000000..aae5d443d7
--- /dev/null
+++ b/react_on_rails_pro/rakelib/rbs.rake
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "open3"
+require "timeout"
+
+# NOTE: Pro package does not include Steep tasks (:steep, :all) as it does not
+# use Steep type checker. Only RBS validation is performed.
+# rubocop:disable Metrics/BlockLength
+namespace :rbs do
+  desc "Validate RBS type signatures"
+  task :validate do
+    require "rbs"
+    require "rbs/cli"
+
+    puts "Validating RBS type signatures..."
+
+    # Use Open3 for better error handling - captures stdout, stderr, and exit status separately
+    # This allows us to distinguish between actual validation errors and warnings
+    # Note: Must use bundle exec even though rake runs in bundle context because
+    # spawned shell commands via Open3.capture3() do NOT inherit bundle context
+    # Wrap in Timeout to prevent hung processes in CI environments (60 second timeout)
+    stdout, stderr, status = Timeout.timeout(60) do
+      Open3.capture3("bundle exec rbs -I sig validate")
+    end
+
+    if status.success?
+      puts "✓ RBS validation passed"
+    else
+      puts "✗ RBS validation failed"
+      puts stdout unless stdout.empty?
+      warn stderr unless stderr.empty?
+      exit 1
+    end
+  end
+
+  desc "Check RBS type signatures (alias for validate)"
+  task check: :validate
+
+  desc "List all RBS files"
+  task :list do
+    sig_files = Dir.glob("sig/**/*.rbs")
+    puts "RBS type signature files:"
+    sig_files.each { |f| puts "  #{f}" }
+    puts "\nTotal: #{sig_files.count} files"
+  end
+end
+# rubocop:enable Metrics/BlockLength
diff --git a/react_on_rails_pro/sig/react_on_rails_pro.rbs b/react_on_rails_pro/sig/react_on_rails_pro.rbs
new file mode 100644
index 0000000000..21e748bae8
--- /dev/null
+++ b/react_on_rails_pro/sig/react_on_rails_pro.rbs
@@ -0,0 +1,5 @@
+module ReactOnRailsPro
+  def self.configure: () { (Configuration) -> void } -> void
+
+  def self.configuration: () -> Configuration
+end
diff --git a/react_on_rails_pro/sig/react_on_rails_pro/cache.rbs b/react_on_rails_pro/sig/react_on_rails_pro/cache.rbs
new file mode 100644
index 0000000000..07509a7aa9
--- /dev/null
+++ b/react_on_rails_pro/sig/react_on_rails_pro/cache.rbs
@@ -0,0 +1,13 @@
+module ReactOnRailsPro
+  class Cache
+    def self.fetch_react_component: (String component_name, Hash[Symbol, untyped] options) { () -> untyped } -> untyped
+
+    def self.use_cache?: (Hash[Symbol, untyped] options) -> bool
+
+    def self.base_cache_key: (String type, ?prerender: bool?) -> Array[String]
+
+    def self.dependencies_cache_key: () -> String?
+
+    def self.react_component_cache_key: (String component_name, Hash[Symbol, untyped] options) -> Array[untyped]
+  end
+end
diff --git a/react_on_rails_pro/sig/react_on_rails_pro/configuration.rbs b/react_on_rails_pro/sig/react_on_rails_pro/configuration.rbs
new file mode 100644
index 0000000000..72ccd567da
--- /dev/null
+++ b/react_on_rails_pro/sig/react_on_rails_pro/configuration.rbs
@@ -0,0 +1,100 @@
+module ReactOnRailsPro
+  class Configuration
+    DEFAULT_RENDERER_URL: String
+    DEFAULT_RENDERER_METHOD: String
+    DEFAULT_RENDERER_FALLBACK_EXEC_JS: bool
+    DEFAULT_RENDERER_HTTP_POOL_SIZE: Integer
+    DEFAULT_RENDERER_HTTP_POOL_TIMEOUT: Integer
+    DEFAULT_RENDERER_HTTP_POOL_WARN_TIMEOUT: Float
+    DEFAULT_SSR_TIMEOUT: Integer
+    DEFAULT_PRERENDER_CACHING: bool
+    DEFAULT_TRACING: bool
+    DEFAULT_DEPENDENCY_GLOBS: Array[String]
+    DEFAULT_EXCLUDED_DEPENDENCY_GLOBS: Array[String]
+    DEFAULT_REMOTE_BUNDLE_CACHE_ADAPTER: nil
+    DEFAULT_RENDERER_REQUEST_RETRY_LIMIT: Integer
+    DEFAULT_THROW_JS_ERRORS: bool
+    DEFAULT_RENDERING_RETURNS_PROMISES: bool
+    DEFAULT_PROFILE_SERVER_RENDERING_JS_CODE: bool
+    DEFAULT_RAISE_NON_SHELL_SERVER_RENDERING_ERRORS: bool
+    DEFAULT_ENABLE_RSC_SUPPORT: bool
+    DEFAULT_RSC_PAYLOAD_GENERATION_URL_PATH: String
+    DEFAULT_RSC_BUNDLE_JS_FILE: String
+    DEFAULT_REACT_CLIENT_MANIFEST_FILE: String
+    DEFAULT_REACT_SERVER_CLIENT_MANIFEST_FILE: String
+
+    attr_accessor renderer_url: String?
+    attr_accessor renderer_password: String?
+    attr_accessor tracing: bool?
+    attr_accessor server_renderer: String?
+    attr_accessor renderer_use_fallback_exec_js: bool?
+    attr_accessor prerender_caching: bool?
+    attr_accessor renderer_http_pool_size: Integer?
+    attr_accessor renderer_http_pool_timeout: Integer?
+    attr_accessor renderer_http_pool_warn_timeout: Float?
+    attr_accessor dependency_globs: Array[String]?
+    attr_accessor excluded_dependency_globs: Array[String]?
+    attr_accessor rendering_returns_promises: bool?
+    attr_accessor remote_bundle_cache_adapter: Module?
+    attr_accessor ssr_pre_hook_js: String?
+    attr_accessor assets_to_copy: Array[String]?
+    attr_accessor renderer_request_retry_limit: Integer?
+    attr_accessor throw_js_errors: bool?
+    attr_accessor ssr_timeout: Integer?
+    attr_accessor profile_server_rendering_js_code: bool?
+    attr_accessor raise_non_shell_server_rendering_errors: bool?
+    attr_accessor enable_rsc_support: bool?
+    attr_accessor rsc_payload_generation_url_path: String?
+    attr_accessor rsc_bundle_js_file: String?
+    attr_accessor react_client_manifest_file: String?
+    attr_accessor react_server_client_manifest_file: String?
+
+    def initialize: (
+      ?renderer_url: String?,
+      ?renderer_password: String?,
+      ?server_renderer: String?,
+      ?renderer_use_fallback_exec_js: bool?,
+      ?prerender_caching: bool?,
+      ?renderer_http_pool_size: Integer?,
+      ?renderer_http_pool_timeout: Integer?,
+      ?renderer_http_pool_warn_timeout: Float?,
+      ?tracing: bool?,
+      ?dependency_globs: Array[String]?,
+      ?excluded_dependency_globs: Array[String]?,
+      ?rendering_returns_promises: bool?,
+      ?remote_bundle_cache_adapter: Module?,
+      ?ssr_pre_hook_js: String?,
+      ?assets_to_copy: Array[String]?,
+      ?renderer_request_retry_limit: Integer?,
+      ?throw_js_errors: bool?,
+      ?ssr_timeout: Integer?,
+      ?profile_server_rendering_js_code: bool?,
+      ?raise_non_shell_server_rendering_errors: bool?,
+      ?enable_rsc_support: bool?,
+      ?rsc_payload_generation_url_path: String?,
+      ?rsc_bundle_js_file: String?,
+      ?react_client_manifest_file: String?,
+      ?react_server_client_manifest_file: String?
+    ) -> void
+
+    def setup_config_values: () -> void
+
+    def check_react_on_rails_support_for_rsc: () -> void
+
+    def setup_execjs_profiler_if_needed: () -> void
+
+    def node_renderer?: () -> bool
+
+    private
+
+    def setup_assets_to_copy: () -> void
+
+    def configure_default_url_if_not_provided: () -> void
+
+    def validate_url: () -> void
+
+    def validate_remote_bundle_cache_adapter: () -> void
+
+    def setup_renderer_password: () -> void
+  end
+end
diff --git a/react_on_rails_pro/sig/react_on_rails_pro/error.rbs b/react_on_rails_pro/sig/react_on_rails_pro/error.rbs
new file mode 100644
index 0000000000..65d7b7d103
--- /dev/null
+++ b/react_on_rails_pro/sig/react_on_rails_pro/error.rbs
@@ -0,0 +1,4 @@
+module ReactOnRailsPro
+  class Error < StandardError
+  end
+end
diff --git a/react_on_rails_pro/sig/react_on_rails_pro/utils.rbs b/react_on_rails_pro/sig/react_on_rails_pro/utils.rbs
new file mode 100644
index 0000000000..908bfd3416
--- /dev/null
+++ b/react_on_rails_pro/sig/react_on_rails_pro/utils.rbs
@@ -0,0 +1,7 @@
+module ReactOnRailsPro
+  module Utils
+    def self.bundle_js_file_path: (String bundle_name) -> String
+
+    def self.running_on_windows?: () -> bool
+  end
+end
diff --git a/sig/react_on_rails.rbs b/sig/react_on_rails.rbs
index 116f0a2e5b..75907bbd10 100644
--- a/sig/react_on_rails.rbs
+++ b/sig/react_on_rails.rbs
@@ -9,30 +9,9 @@ module ReactOnRails
   def self.configure: () { (Configuration) -> void } -> void
   def self.configuration: () -> Configuration
 
+  # Error classes are defined in separate RBS files:
+  # - sig/react_on_rails/prerender_error.rbs
+  # - sig/react_on_rails/json_parse_error.rbs
   class Error < StandardError
   end
-
-  class PrerenderError < Error
-    attr_reader component_name: String?
-    attr_reader js_code: String?
-    attr_reader err: Hash[Symbol, untyped]?
-    attr_reader props: (Hash[Symbol, untyped] | String)?
-    attr_reader console_messages: Array[String]?
-
-    def initialize: (
-      ?component_name: String?,
-      ?js_code: String?,
-      ?err: Hash[Symbol, untyped]?,
-      ?props: (Hash[Symbol, untyped] | String)?,
-      ?console_messages: Array[String]?
-    ) -> void
-
-    def to_honeybadger_context: () -> Hash[Symbol, untyped]
-    def raven_context: () -> Hash[Symbol, untyped]
-    def to_error_context: () -> Hash[Symbol, untyped]
-  end
-
-  class JsonParseError < Error
-    def initialize: (Hash[Symbol, untyped] err) -> void
-  end
 end
diff --git a/spec/react_on_rails/rake_tasks_spec.rb b/spec/react_on_rails/rake_tasks_spec.rb
new file mode 100644
index 0000000000..e8dfc67525
--- /dev/null
+++ b/spec/react_on_rails/rake_tasks_spec.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require "rake"
+
+RSpec.describe "RBS Rake Tasks" do
+  before do
+    # Load the rake tasks file
+    load File.expand_path("../../rakelib/rbs.rake", __dir__)
+  end
+
+  describe "rake rbs:validate" do
+    it "is defined" do
+      expect(Rake::Task.task_defined?("rbs:validate")).to be true
+    end
+
+    it "is a rake task" do
+      task = Rake::Task["rbs:validate"]
+      expect(task).to be_a(Rake::Task)
+    end
+  end
+
+  describe "rake rbs:check" do
+    it "is defined as alias for validate" do
+      expect(Rake::Task.task_defined?("rbs:check")).to be true
+    end
+
+    it "depends on validate task" do
+      task = Rake::Task["rbs:check"]
+      # Prerequisites are stored without namespace when defined with task name: :prerequisite
+      expect(task.prerequisites).to include("validate")
+    end
+  end
+
+  describe "rake rbs:steep" do
+    it "is defined" do
+      expect(Rake::Task.task_defined?("rbs:steep")).to be true
+    end
+
+    it "is a rake task" do
+      task = Rake::Task["rbs:steep"]
+      expect(task).to be_a(Rake::Task)
+    end
+  end
+
+  describe "rake rbs:list" do
+    it "is defined" do
+      expect(Rake::Task.task_defined?("rbs:list")).to be true
+    end
+
+    it "is a rake task" do
+      task = Rake::Task["rbs:list"]
+      expect(task).to be_a(Rake::Task)
+    end
+  end
+
+  describe "rake rbs:all" do
+    it "is defined" do
+      expect(Rake::Task.task_defined?("rbs:all")).to be true
+    end
+
+    it "depends on validate and steep tasks" do
+      task = Rake::Task["rbs:all"]
+      # Prerequisites are stored without namespace when defined with task name: :prerequisite
+      expect(task.prerequisites).to include("validate", "steep")
+    end
+  end
+end
diff --git a/spec/react_on_rails/rbs_runtime_checking_spec.rb b/spec/react_on_rails/rbs_runtime_checking_spec.rb
new file mode 100644
index 0000000000..c2def8e891
--- /dev/null
+++ b/spec/react_on_rails/rbs_runtime_checking_spec.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require_relative "spec_helper"
+
+# This spec validates that RBS runtime type checking catches actual type violations
+# when enabled during test execution. These tests should only run when RBS is available.
+RSpec.describe "RBS Runtime Type Checking", type: :rbs do
+  before do
+    skip "RBS gem not available" unless defined?(RBS)
+    skip "RBS runtime checking disabled" if ENV["DISABLE_RBS_RUNTIME_CHECKING"] == "true"
+    skip "RBS runtime hook not loaded" unless ENV.fetch("RUBYOPT", "").include?("-rrbs/test/setup")
+  end
+
+  describe "Configuration type checking" do
+    it "catches invalid type assignments to configuration" do
+      # This test verifies runtime checking actually works by intentionally
+      # violating a type signature and expecting RBS to catch it
+      #
+      # Type signature defined in: sig/react_on_rails/configuration.rbs
+      #   attr_accessor server_bundle_js_file: String
+      #
+      # When RBS runtime checking is enabled via rakelib/run_rspec.rake, the
+      # RBS::Test::Hook wraps all method calls to ReactOnRails classes and validates
+      # that arguments and return values match the type signatures.
+      expect do
+        config = ReactOnRails::Configuration.new(
+          server_bundle_js_file: 123 # Invalid: should be String, not Integer
+        )
+        config.server_bundle_js_file # Access to trigger type check
+      end.to raise_error(RBS::Test::Hook::TypeError)
+    end
+
+    it "allows valid type assignments to configuration" do
+      # This validates that correct types pass through without error
+      expect do
+        config = ReactOnRails::Configuration.new(
+          server_bundle_js_file: "valid-string.js"
+        )
+        config.server_bundle_js_file
+      end.not_to raise_error
+    end
+  end
+
+  describe "Helper method type checking" do
+    # Test that helper methods have their signatures validated
+    # This ensures the RBS signatures in sig/ are being used
+    it "has RBS signatures loaded for ReactOnRails::Helper" do
+      # Verify the helper module has type signatures
+      expect(ReactOnRails::Helper).to be_a(Module)
+
+      # If RBS runtime checking is active, method calls will be wrapped
+      # We can verify this by checking that invalid calls raise type errors
+      # (implementation depends on specific helper method signatures)
+    end
+  end
+
+  describe "RBS::Test environment" do
+    it "has RBS_TEST_TARGET configured for ReactOnRails" do
+      expect(ENV.fetch("RBS_TEST_TARGET", "")).to include("ReactOnRails")
+    end
+
+    it "has loaded RBS test setup" do
+      # Verify the RBS test framework is active
+      expect(defined?(RBS::Test::Hook)).to be_truthy
+    end
+  end
+end