diff --git a/src/main/java/org/opensearch/agent/ToolPlugin.java b/src/main/java/org/opensearch/agent/ToolPlugin.java
index 823320f0..fb3d63f7 100644
--- a/src/main/java/org/opensearch/agent/ToolPlugin.java
+++ b/src/main/java/org/opensearch/agent/ToolPlugin.java
@@ -15,6 +15,7 @@
 import org.opensearch.agent.tools.CreateAnomalyDetectorTool;
 import org.opensearch.agent.tools.NeuralSparseSearchTool;
 import org.opensearch.agent.tools.PPLTool;
+import org.opensearch.agent.tools.PainlessTool;
 import org.opensearch.agent.tools.RAGTool;
 import org.opensearch.agent.tools.SearchAlertsTool;
 import org.opensearch.agent.tools.SearchAnomalyDetectorsTool;
@@ -77,6 +78,7 @@ public Collection<Object> createComponents(
         SearchMonitorsTool.Factory.getInstance().init(client);
         CreateAlertTool.Factory.getInstance().init(client);
         CreateAnomalyDetectorTool.Factory.getInstance().init(client);
+        PainlessTool.Factory.getInstance().init(scriptService);
         return Collections.emptyList();
     }
 
@@ -93,7 +95,8 @@ public List<Tool.Factory<? extends Tool>> getToolFactories() {
                 SearchAnomalyResultsTool.Factory.getInstance(),
                 SearchMonitorsTool.Factory.getInstance(),
                 CreateAlertTool.Factory.getInstance(),
-                CreateAnomalyDetectorTool.Factory.getInstance()
+                CreateAnomalyDetectorTool.Factory.getInstance(),
+                PainlessTool.Factory.getInstance()
             );
     }
 
diff --git a/src/main/java/org/opensearch/agent/tools/PainlessTool.java b/src/main/java/org/opensearch/agent/tools/PainlessTool.java
new file mode 100644
index 00000000..4f04fad9
--- /dev/null
+++ b/src/main/java/org/opensearch/agent/tools/PainlessTool.java
@@ -0,0 +1,150 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.agent.tools;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.opensearch.core.action.ActionListener;
+import org.opensearch.ml.common.spi.tools.Tool;
+import org.opensearch.ml.common.spi.tools.ToolAnnotation;
+import org.opensearch.script.Script;
+import org.opensearch.script.ScriptService;
+import org.opensearch.script.ScriptType;
+import org.opensearch.script.TemplateScript;
+
+import com.google.gson.Gson;
+
+import lombok.Getter;
+import lombok.Setter;
+import lombok.extern.log4j.Log4j2;
+
+/**
+ * use case for this tool will only focus on flow agent
+ */
+@Log4j2
+@Setter
+@Getter
+@ToolAnnotation(PainlessTool.TYPE)
+public class PainlessTool implements Tool {
+    public static final String TYPE = "PainlessTool";
+    private static final String DEFAULT_DESCRIPTION = "Use this tool to execute painless script";
+
+    @Setter
+    @Getter
+    private String name = TYPE;
+
+    @Getter
+    private String type = TYPE;
+
+    @Getter
+    @Setter
+    private String description = DEFAULT_DESCRIPTION;
+
+    @Getter
+    private String version;
+
+    private ScriptService scriptService;
+    @Setter
+    private String scriptCode;
+
+    public PainlessTool(ScriptService scriptEngine, String script) {
+        this.scriptService = scriptEngine;
+        this.scriptCode = script;
+    }
+
+    private Gson gson = new Gson();
+
+    @Override
+    public <T> void run(Map<String, String> parameters, ActionListener<T> listener) {
+        Script script = new Script(ScriptType.INLINE, "painless", scriptCode, Collections.emptyMap());
+        Map<String, Object> flattenedParameters = new HashMap<>();
+        for (Map.Entry<String, String> entry : parameters.entrySet()) {
+            // keep original values and flatten
+            flattenedParameters.put(entry.getKey(), entry.getValue());
+            // TODO default is json parser. we may support format
+            try {
+                String value = org.apache.commons.text.StringEscapeUtils.unescapeJson(entry.getValue());
+                Map<String, ?> map = gson.fromJson(value, Map.class);
+                flattenMap(map, flattenedParameters, entry.getKey());
+            } catch (Throwable ignored) {}
+        }
+        TemplateScript templateScript = scriptService.compile(script, TemplateScript.CONTEXT).newInstance(flattenedParameters);
+        try {
+            String result = templateScript.execute();
+            listener.onResponse(result == null ? (T) "" : (T) result);
+        } catch (Exception e) {
+            listener.onFailure(e);
+        }
+    }
+
+    private void flattenMap(Map<String, ?> map, Map<String, Object> flatMap, String prefix) {
+        for (Map.Entry<String, ?> entry : map.entrySet()) {
+            String key = entry.getKey();
+            if (prefix != null && !prefix.isEmpty()) {
+                key = prefix + "." + entry.getKey();
+            }
+            Object value = entry.getValue();
+            if (value instanceof Map) {
+                flattenMap((Map<String, ?>) value, flatMap, key);
+            } else {
+                flatMap.put(key, value);
+            }
+        }
+    }
+
+    @Override
+    public boolean validate(Map<String, String> map) {
+        return true;
+    }
+
+    public static class Factory implements Tool.Factory<PainlessTool> {
+        private ScriptService scriptService;
+
+        private static PainlessTool.Factory INSTANCE;
+
+        public static PainlessTool.Factory getInstance() {
+            if (INSTANCE != null) {
+                return INSTANCE;
+            }
+            synchronized (PainlessTool.class) {
+                if (INSTANCE != null) {
+                    return INSTANCE;
+                }
+                INSTANCE = new PainlessTool.Factory();
+                return INSTANCE;
+            }
+        }
+
+        public void init(ScriptService scriptService) {
+            this.scriptService = scriptService;
+        }
+
+        @Override
+        public PainlessTool create(Map<String, Object> map) {
+            String script = (String) map.get("script");
+            // TODO add script non null/empty check
+            return new PainlessTool(scriptService, script);
+        }
+
+        @Override
+        public String getDefaultDescription() {
+            return DEFAULT_DESCRIPTION;
+        }
+
+        @Override
+        public String getDefaultType() {
+            return TYPE;
+        }
+
+        @Override
+        public String getDefaultVersion() {
+            return null;
+        }
+
+    }
+}
diff --git a/src/test/java/org/opensearch/integTest/PainlessToolIT.java b/src/test/java/org/opensearch/integTest/PainlessToolIT.java
new file mode 100644
index 00000000..84659d12
--- /dev/null
+++ b/src/test/java/org/opensearch/integTest/PainlessToolIT.java
@@ -0,0 +1,79 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.integTest;
+
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import org.junit.Assert;
+import org.junit.Before;
+
+import lombok.SneakyThrows;
+import lombok.extern.log4j.Log4j2;
+
+@Log4j2
+public class PainlessToolIT extends BaseAgentToolsIT {
+
+    private String registerAgentRequestBody;
+
+    @Before
+    @SneakyThrows
+    public void setUp() {
+        super.setUp();
+        registerAgentRequestBody = Files
+            .readString(
+                Path.of(this.getClass().getClassLoader().getResource("org/opensearch/agent/tools/register_painless_agent.json").toURI())
+            );
+    }
+
+    public void test_execute() {
+        String script = "def x = new HashMap(); x.abc = '5'; return x.abc;";
+        String agentRequestBody = registerAgentRequestBody.replaceAll("<SCRIPT>", script);
+        String agentId = createAgent(agentRequestBody);
+        String agentInput = "{\"parameters\":{}}";
+        String result = executeAgent(agentId, agentInput);
+        Assert.assertEquals("5", result);
+    }
+
+    public void test_execute_with_parameter() {
+        String script = "params.x + params.y";
+        String agentRequestBody = registerAgentRequestBody.replaceAll("<SCRIPT>", script);
+        String agentId = createAgent(agentRequestBody);
+        String agentInput = "{\"parameters\":{\"x\":1,\"y\":2}}";
+        String result = executeAgent(agentId, agentInput);
+        Assert.assertEquals("12", result);
+    }
+
+    public void test_execute_with_parameter2() throws URISyntaxException, IOException {
+        String script =
+            "return 'An example output: with ppl:<ppl>' + params.get('PPL.output.ppl') + '</ppl>, and this is ppl result: <ppl_result>' + params.get('PPL.output.executionResult') + '</ppl_result>'";
+        String mockPPLOutput = "return '{\\\\\"executionResult\\\\\":\\\\\"result\\\\\",\\\\\"ppl\\\\\":\\\\\"source=demo| head 1\\\\\"}'";
+        String registerAgentRequestBody2 = Files
+            .readString(
+                Path
+                    .of(
+                        this
+                            .getClass()
+                            .getClassLoader()
+                            .getResource("org/opensearch/agent/tools/register_painless_agent_with_multiple_tools.json")
+                            .toURI()
+                    )
+            );
+        String agentRequestBody = registerAgentRequestBody2.replaceAll("<SCRIPT1>", mockPPLOutput).replaceAll("<SCRIPT2>", script);
+
+        log.info("agentRequestBody = {}", agentRequestBody);
+        String agentId = createAgent(agentRequestBody);
+        String agentInput = "{\"parameters\":{}}";
+        String result = executeAgent(agentId, agentInput);
+        Assert
+            .assertEquals(
+                "An example output: with ppl:<ppl>source=demo| head 1</ppl>, and this is ppl result: <ppl_result>result</ppl_result>",
+                result
+            );
+    }
+}
diff --git a/src/test/resources/org/opensearch/agent/tools/register_painless_agent.json b/src/test/resources/org/opensearch/agent/tools/register_painless_agent.json
new file mode 100644
index 00000000..965f09b8
--- /dev/null
+++ b/src/test/resources/org/opensearch/agent/tools/register_painless_agent.json
@@ -0,0 +1,12 @@
+{
+  "name": "Test_PainlessTool",
+  "type": "flow",
+  "tools": [
+    {
+      "type": "PainlessTool",
+      "parameters": {
+        "script": "<SCRIPT>"
+      }
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/test/resources/org/opensearch/agent/tools/register_painless_agent_with_multiple_tools.json b/src/test/resources/org/opensearch/agent/tools/register_painless_agent_with_multiple_tools.json
new file mode 100644
index 00000000..ae100a89
--- /dev/null
+++ b/src/test/resources/org/opensearch/agent/tools/register_painless_agent_with_multiple_tools.json
@@ -0,0 +1,19 @@
+{
+  "name": "Test_PainlessTool",
+  "type": "flow",
+  "tools": [
+    {
+      "type": "PainlessTool",
+      "name": "PPL",
+      "parameters": {
+        "script": "<SCRIPT1>"
+      }
+    },
+    {
+      "type": "PainlessTool",
+      "parameters": {
+        "script": "<SCRIPT2>"
+      }
+    }
+  ]
+}
\ No newline at end of file