diff --git a/.github/workflows/sdk-spec.yml b/.github/workflows/sdk-spec.yml
new file mode 100644
index 0000000..270f0d3
--- /dev/null
+++ b/.github/workflows/sdk-spec.yml
@@ -0,0 +1,17 @@
+name: SDK spec
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  sdk-spec:
+    # Keep the ref in `uses:` and `spec-ref` in sync.
+    uses: Flagsmith/sdk-spec/.github/workflows/run-spec.yml@v0.3.0
+    with:
+      spec-ref: v0.3.0
+      language: ruby
diff --git a/flagsmith.gemspec b/flagsmith.gemspec
index a1e9459..adbe62a 100644
--- a/flagsmith.gemspec
+++ b/flagsmith.gemspec
@@ -12,7 +12,7 @@ Gem::Specification.new do |spec|
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
   spec.files = Dir.chdir(__dir__) do
     `git ls-files -z`.split("\x0").reject do |f|
-      (f == __FILE__) || f.match(%r{\A(?:(?:bin|test|spec|features)/|\.(?:git|travis|circleci)|appveyor)})
+      (f == __FILE__) || f.match(%r{\A(?:(?:bin|test|spec|sdk-spec|features)/|\.(?:git|travis|circleci)|appveyor)})
     end
   end
 
diff --git a/renovate.json b/renovate.json
index b7a5f2e..b1830e2 100644
--- a/renovate.json
+++ b/renovate.json
@@ -4,6 +4,15 @@
     "ignorePresets": [":semanticPrefixFixDepsChoreOthers"],
     "semanticCommitType": "deps",
     "git-submodules": { "enabled": true },
+    "customManagers": [
+        {
+            "customType": "regex",
+            "managerFilePatterns": ["/^\\.github/workflows/sdk-spec\\.yml$/"],
+            "matchStrings": ["spec-ref: (?<currentValue>v[\\d.]+)"],
+            "depNameTemplate": "Flagsmith/sdk-spec",
+            "datasourceTemplate": "github-tags"
+        }
+    ],
     "packageRules": [
         {
             "matchUpdateTypes": [
@@ -23,6 +32,11 @@
             "matchManagers": ["git-submodules"],
             "versioning": "semver-coerced",
             "enabled": true
+        },
+        {
+            "matchPackageNames": ["Flagsmith/sdk-spec"],
+            "groupName": "SDK spec",
+            "enabled": true
         }
     ]
 }
diff --git a/sdk-spec/Dockerfile b/sdk-spec/Dockerfile
new file mode 100644
index 0000000..87527e4
--- /dev/null
+++ b/sdk-spec/Dockerfile
@@ -0,0 +1,17 @@
+# Runs this SDK, built from source, under the Flagsmith SDK behavioural spec.
+# docker build -f sdk-spec/Dockerfile --build-context harness=<sdk-spec>/harness/ruby .
+FROM docker.io/library/ruby:3.3-slim
+
+# The gemspec lists its files with `git ls-files`.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends git \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /sdk
+COPY . .
+RUN gem build flagsmith.gemspec --output flagsmith.gem \
+    && gem install --no-document flagsmith.gem
+
+COPY --from=harness harness.rb /harness/harness.rb
+
+ENTRYPOINT ["ruby", "/harness/harness.rb", "sdk-spec/steps.rb"]
diff --git a/sdk-spec/steps.rb b/sdk-spec/steps.rb
new file mode 100644
index 0000000..aed63d9
--- /dev/null
+++ b/sdk-spec/steps.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+# Steps for the Flagsmith SDK behavioural spec: https://github.com/Flagsmith/sdk-spec
+#
+# Each method implements the Gherkin step in the comment above it.
+
+require 'flagsmith'
+
+def as_spec_flags(flags)
+  flags.all_flags.map do |flag|
+    { feature: flag.feature_name, enabled: flag.enabled, value: flag.value }
+  end
+end
+
+# Create the SDK client
+def create_client(environment_key, api_url)
+  Flagsmith::Client.new(environment_key: environment_key, api_url: api_url)
+end
+
+# When the application gets the environment flags
+def get_environment_flags(flagsmith)
+  as_spec_flags(flagsmith.get_environment_flags)
+end
+
+# When the application gets the flags for identity "{identifier}" with traits:
+def get_identity_flags(flagsmith, identifier, traits)
+  as_spec_flags(flagsmith.get_identity_flags(identifier, **traits))
+end