diff --git a/.github/workflows/sdk-spec.yml b/.github/workflows/sdk-spec.yml
new file mode 100644
index 0000000..7ad90ac
--- /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: java
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..4b5e7ed
--- /dev/null
+++ b/sdk-spec/Dockerfile
@@ -0,0 +1,24 @@
+# Runs this SDK, built from source, under the Flagsmith SDK behavioural spec.
+# docker build -f sdk-spec/Dockerfile --build-context harness=<sdk-spec>/harness/java .
+FROM docker.io/library/maven:3.9-eclipse-temurin-11 AS build
+
+WORKDIR /sdk
+COPY pom.xml lombok.config ./
+COPY src/main ./src/main
+RUN mvn --batch-mode --no-transfer-progress \
+      -Dmaven.test.skip=true -Dcheckstyle.skip=true -Djacoco.skip=true -Dmaven.source.skip=true \
+      package dependency:copy-dependencies -DincludeScope=runtime -DoutputDirectory=target/lib \
+ && cp target/flagsmith-java-client-*.jar target/lib/
+
+COPY --from=harness Harness.java /harness/Harness.java
+COPY sdk-spec/Steps.java ./sdk-spec/Steps.java
+RUN javac -cp "target/lib/*" -d target/classes-spec /harness/Harness.java sdk-spec/Steps.java
+
+FROM docker.io/library/eclipse-temurin:11-jre
+
+WORKDIR /sdk
+COPY --from=build /sdk/target/lib ./lib
+COPY --from=build /sdk/target/classes-spec ./classes
+COPY sdk-spec/Steps.java ./sdk-spec/Steps.java
+
+ENTRYPOINT ["java", "-XX:TieredStopAtLevel=1", "-cp", "classes:lib/*", "Harness", "sdk-spec/Steps.java"]
diff --git a/sdk-spec/Steps.java b/sdk-spec/Steps.java
new file mode 100644
index 0000000..f5d80d4
--- /dev/null
+++ b/sdk-spec/Steps.java
@@ -0,0 +1,50 @@
+import com.flagsmith.FlagsmithClient;
+import com.flagsmith.exceptions.FlagsmithClientError;
+import com.flagsmith.models.BaseFlag;
+import com.flagsmith.models.Flags;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Steps for the Flagsmith SDK behavioural spec: https://github.com/Flagsmith/sdk-spec
+ *
+ * <p>Each method implements the Gherkin step in the comment above it.
+ */
+public class Steps {
+
+  /** A flag in the shape the spec expects. */
+  public static class SpecFlag {
+    public final String feature;
+    public final boolean enabled;
+    public final Object value;
+
+    SpecFlag(BaseFlag flag) {
+      feature = flag.getFeatureName();
+      enabled = flag.getEnabled();
+      value = flag.getValue();
+    }
+  }
+
+  static List<SpecFlag> asSpecFlags(Flags flags) {
+    return flags.getAllFlags().stream().map(SpecFlag::new).collect(Collectors.toList());
+  }
+
+  // Create the SDK client
+  static FlagsmithClient createClient(String environmentKey, String apiUrl) {
+    return FlagsmithClient.newBuilder().setApiKey(environmentKey).withApiUrl(apiUrl).build();
+  }
+
+  // When the application gets the environment flags
+  static List<SpecFlag> getEnvironmentFlags(FlagsmithClient flagsmith)
+      throws FlagsmithClientError {
+    return asSpecFlags(flagsmith.getEnvironmentFlags());
+  }
+
+  // When the application gets the flags for identity "{identifier}" with traits:
+  static List<SpecFlag> getIdentityFlags(
+      FlagsmithClient flagsmith, String identifier, Map<String, Object> traits)
+      throws FlagsmithClientError {
+    return asSpecFlags(flagsmith.getIdentityFlags(identifier, traits));
+  }
+}