@@ -21,11 +21,34 @@
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-api</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.jspecify</groupId>
+            <artifactId>jspecify</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>
@@ -0,0 +1,75 @@
+package org.a2aproject.sdk.common.logging;
+
+/**
+ * Enumeration of A2A protocol payload event types for structured logging.
+ * <p>
+ * Each event type corresponds to a category of protocol message that can be
+ * logged with structured fields for observability and debugging.
+ * </p>
+ */
+public enum A2AEventType {
+    /**
+     * Task request: message/send, message/stream, getTask, listTasks, cancelTask, etc.
+     */
+    TASK_REQUEST("task.request"),
+
+    /**
+     * Task state change: TaskStatusUpdateEvent and status transitions.
+     */
+    STATE_CHANGE("task.state_change"),
+
+    /**
+     * Result artifact: TaskArtifactUpdateEvent and artifact payloads.
+     */
+    ARTIFACT("task.artifact"),
+
+    /**
+     * Task result: final Task snapshot returned to client.
+     */
+    TASK_RESULT("task.result"),
+
+    /**
+     * Negotiation payload: extension negotiation, version negotiation, AgentCard capabilities.
+     */
+    NEGOTIATION("negotiation"),
+
+    /**
+     * Authorization decision: allow/deny from TaskAuthorizationProvider.
+     */
+    AUTHORIZATION("authorization"),
+
+    /**
+     * Notification subscription: push config create/get/list/delete, subscribeToTask.
+     */
+    NOTIFICATION_SUBSCRIPTION("notification.subscription"),
+
+    /**
+     * Notification delivery: push webhook dispatch to external URL.
+     */
+    NOTIFICATION_DELIVERY("notification.delivery"),
+
+    /**
+     * Streaming event: per-event SSE streaming payload.
+     */
+    STREAMING_EVENT("streaming.event"),
+
+    /**
+     * Generic payload for any other structured log.
+     */
+    GENERIC("generic");
+
+    private final String value;
+
+    A2AEventType(String value) {
+        this.value = value;
+    }
+
+    public String value() {
+        return value;
+    }
+
+    @Override
+    public String toString() {
+        return value;
+    }
+}
@@ -0,0 +1,174 @@
+package org.a2aproject.sdk.common.logging;
+
+import java.util.Set;
+
+import org.jspecify.annotations.Nullable;
+
+/**
+ * Configuration for structured payload logging.
+ * <p>
+ * Supports both system properties and programmatic configuration via builder.
+ * </p>
+ * <h2>System Properties</h2>
+ * <ul>
+ *   <li>{@code a2a.logging.payload.enabled} (boolean, default false) — enable payload logging</li>
+ *   <li>{@code a2a.logging.payload.max-size} (int, default 4096) — max payload size before truncation</li>
+ *   <li>{@code a2a.logging.payload.masking.enabled} (boolean, default true) — enable sensitive masking</li>
+ *   <li>{@code a2a.logging.payload.masking.strategy} (class name) — custom masking strategy</li>
+ * </ul>
+ */
+public final class A2APayloadLoggingConfig {
+
+    public static final String ENABLED_PROPERTY = "a2a.logging.payload.enabled";
+    public static final String MAX_SIZE_PROPERTY = "a2a.logging.payload.max-size";
+    public static final String MASKING_ENABLED_PROPERTY = "a2a.logging.payload.masking.enabled";
+    public static final String MASKING_STRATEGY_PROPERTY = "a2a.logging.payload.masking.strategy";
+    public static final String MASKING_SENSITIVE_KEYS_PROPERTY = "a2a.logging.payload.masking.sensitive-keys";
+    public static final int DEFAULT_MAX_SIZE = 4096;
+
+    private final boolean enabled;
+    private final int maxSize;
+    private final boolean maskingEnabled;
+    private final @Nullable PayloadMaskingStrategy maskingStrategy;
+    private final @Nullable Set<String> sensitiveKeys;
+
+    private A2APayloadLoggingConfig(Builder builder) {
+        this.enabled = builder.enabled;
+        this.maxSize = builder.maxSize;
+        this.maskingEnabled = builder.maskingEnabled;
+        this.maskingStrategy = builder.maskingStrategy;
+        this.sensitiveKeys = builder.sensitiveKeys;
+    }
+
+    public boolean isEnabled() {
+        return enabled;
+    }
+
+    public int getMaxSize() {
+        return maxSize;
+    }
+
+    public boolean isMaskingEnabled() {
+        return maskingEnabled;
+    }
+
+    public @Nullable PayloadMaskingStrategy getMaskingStrategy() {
+        return maskingStrategy;
+    }
+
+    public @Nullable Set<String> getSensitiveKeys() {
+        return sensitiveKeys;
+    }
+
+    /**
+     * Creates config from system properties.
+     */
+    public static A2APayloadLoggingConfig fromSystemProperties() {
+        Builder builder = new Builder();
+        String enabledProp = System.getProperty(ENABLED_PROPERTY);
+        if (enabledProp != null) {
+            builder.enabled(Boolean.parseBoolean(enabledProp));
+        }
+        String maxSizeProp = System.getProperty(MAX_SIZE_PROPERTY);
+        if (maxSizeProp != null) {
+            try {
+                builder.maxSize(Integer.parseInt(maxSizeProp.trim()));
+            } catch (NumberFormatException ignored) {
+                // use default
+            }
+        }
+        String maskingEnabledProp = System.getProperty(MASKING_ENABLED_PROPERTY);
+        if (maskingEnabledProp != null) {
+            builder.maskingEnabled(Boolean.parseBoolean(maskingEnabledProp));
+        }
+        // Strategy loaded separately by logger via ServiceLoader / reflection;
+        // we don't instantiate here to avoid class loading issues in fromSystemProperties
+        String strategyClass = System.getProperty(MASKING_STRATEGY_PROPERTY);
+        if (strategyClass != null && !strategyClass.isBlank()) {
+            try {
+                Class<?> clazz = Class.forName(strategyClass.trim());
+                Object instance = clazz.getDeclaredConstructor().newInstance();
+                if (instance instanceof PayloadMaskingStrategy pms) {
+                    builder.maskingStrategy(pms);
+                }
+            } catch (Exception ignored) {
+            }
+        }
+        String sensitiveKeysProp = System.getProperty(MASKING_SENSITIVE_KEYS_PROPERTY);
+        if (sensitiveKeysProp != null && !sensitiveKeysProp.isBlank()) {
+            Set<String> keys = Set.of(sensitiveKeysProp.split(","));
+            // Trim each key
+            Set<String> trimmed = new java.util.HashSet<>();
+            for (String k : keys) {
+                if (k != null && !k.isBlank()) {
+                    trimmed.add(k.trim());
+                }
+            }
+            if (!trimmed.isEmpty()) {
+                builder.sensitiveKeys(trimmed);
+            }
+        }
+        return builder.build();
+    }
+
+    public Builder toBuilder() {
+        Builder b = new Builder();
+        b.enabled = this.enabled;
+        b.maxSize = this.maxSize;
+        b.maskingEnabled = this.maskingEnabled;
+        b.maskingStrategy = this.maskingStrategy;
+        b.sensitiveKeys = this.sensitiveKeys;
+        return b;
+    }
+
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    public static final class Builder {
+        private boolean enabled = false;
+        private int maxSize = DEFAULT_MAX_SIZE;
+        private boolean maskingEnabled = true;
+        private @Nullable PayloadMaskingStrategy maskingStrategy = null;
+        private @Nullable Set<String> sensitiveKeys = null;
+
+        public Builder enabled(boolean enabled) {
+            this.enabled = enabled;
+            return this;
+        }
+
+        public Builder maxSize(int maxSize) {
+            this.maxSize = maxSize;
+            return this;
+        }
+
+        public Builder maskingEnabled(boolean maskingEnabled) {
+            this.maskingEnabled = maskingEnabled;
+            return this;
+        }
+
+        public Builder maskingStrategy(@Nullable PayloadMaskingStrategy maskingStrategy) {
+            this.maskingStrategy = maskingStrategy;
+            return this;
+        }
+
+        public Builder sensitiveKeys(@Nullable Set<String> sensitiveKeys) {
+            this.sensitiveKeys = sensitiveKeys;
+            return this;
+        }
+
+        public A2APayloadLoggingConfig build() {
+            return new A2APayloadLoggingConfig(this);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "A2APayloadLoggingConfig{"
+                + "enabled=" + enabled
+                + ", maxSize=" + maxSize
+                + ", maskingEnabled=" + maskingEnabled
+                + ", maskingStrategy=" + (maskingStrategy != null ? maskingStrategy.getClass().getName() : "default")
+                + '}';
+    }
+}