diff --git a/ai/ai-samples/src/features/function-calling/index.tsx b/ai/ai-samples/src/features/function-calling/index.tsx
index 83f2c413a..023f110ed 100644
--- a/ai/ai-samples/src/features/function-calling/index.tsx
+++ b/ai/ai-samples/src/features/function-calling/index.tsx
@@ -1,9 +1,136 @@
-import React from 'react';
+import { useState } from 'react';
+import { executeFunctionCalling, FunctionCallingResult } from './service';
+
+export default function FunctionCallingView() {
+  const [prompt, setPrompt] = useState('What was the weather in Boston on October 17, 2024?');
+  const [loading, setLoading] = useState(false);
+  const [result, setResult] = useState<FunctionCallingResult | null>(null);
+  const [error, setError] = useState<string | null>(null);
+
+  const handleRun = async () => {
+    const cleanedPrompt = prompt.trim();
+
+    if (!cleanedPrompt) {
+      setError('Please enter a prompt.');
+      return;
+    }
+
+    setLoading(true);
+    setError(null);
+    setResult(null);
+
+    try {
+      const res = await executeFunctionCalling(cleanedPrompt);
+      setResult(res);
+    } catch (err: unknown) {
+      console.error(err);
+      const message = err instanceof Error ? err.message : 'An error occurred during function calling.';
+      setError(message);
+    } finally {
+      setLoading(false);
+    }
+  };
 
-export default function FunctionCallingFeature() {
   return (
-    <div>
-      <h2>function-calling</h2>
+    <div style={{ padding: '20px', maxWidth: '700px', margin: '0 auto', fontFamily: 'sans-serif' }}>
+      <h2>Function Calling</h2>
+      <p style={{ color: '#666', marginBottom: '20px' }}>
+        Demonstrates the manual round-trip: Gemini extracts structured arguments,
+        your app executes a local function, and sends the result back for final text synthesis.
+      </p>
+
+      {/* Input Prompt */}
+      <div style={{ marginBottom: '15px' }}>
+        <textarea
+          value={prompt}
+          onChange={(e) => setPrompt(e.target.value)}
+          rows={3}
+          style={{
+            width: '100%',
+            padding: '10px',
+            borderRadius: '6px',
+            border: '1px solid #ccc',
+            boxSizing: 'border-box',
+            fontSize: '14px',
+          }}
+          placeholder="Ask a question that triggers the tool..."
+        />
+      </div>
+
+      <button
+        onClick={handleRun}
+        disabled={loading || !prompt.trim()}
+        style={{
+          padding: '10px 20px',
+          backgroundColor: loading ? '#ccc' : '#1a73e8',
+          color: '#fff',
+          border: 'none',
+          borderRadius: '4px',
+          cursor: loading ? 'not-allowed' : 'pointer',
+          fontWeight: 'bold',
+        }}
+      >
+        {loading ? 'Executing Round-Trip...' : 'Run Function Calling'}
+      </button>
+
+      {/* Error Output */}
+      {error && (
+        <div style={{ marginTop: '20px', padding: '12px', backgroundColor: '#fde8e8', color: '#c5221f', borderRadius: '6px' }}>
+          <strong>Error:</strong> {error}
+        </div>
+      )}
+
+      {/* Visual Round-Trip Breakdown */}
+      {result && (
+        <div style={{ marginTop: '25px', display: 'flex', flexDirection: 'column', gap: '15px' }}>
+
+          {/* Step 1 & 2: Function Call Request */}
+          {result.functionCall ? (
+            <div style={{ padding: '15px', border: '1px solid #e0e0e0', borderRadius: '8px', backgroundColor: '#f8f9fa' }}>
+              <h4 style={{ margin: '0 0 8px 0', color: '#1a73e8' }}>
+                Step 1 & 2: Model Triggered Function Call
+              </h4>
+              <p style={{ margin: '0 0 8px 0', fontSize: '13px', color: '#555' }}>
+                Tool Requested: <code>{result.functionCall.name}</code>
+              </p>
+              <pre style={{ margin: 0, padding: '10px', backgroundColor: '#282c34', color: '#abb2bf', borderRadius: '4px', overflowX: 'auto', fontSize: '12px' }}>
+                {JSON.stringify(result.functionCall.args, null, 2)}
+              </pre>
+            </div>
+          ) : (
+            <div style={{ padding: '15px', border: '1px solid #e0e0e0', borderRadius: '8px', backgroundColor: '#fff3cd' }}>
+              <p style={{ margin: 0, color: '#856404' }}>
+              </p>
+            </div>
+          )}
+
+          {/* Step 3: Local Function Output */}
+          {result.functionResult && (
+            <div style={{ padding: '15px', border: '1px solid #e0e0e0', borderRadius: '8px', backgroundColor: '#f8f9fa' }}>
+              <h4 style={{ margin: '0 0 8px 0', color: '#137333' }}>
+                Step 3: Local Function Execution Result
+              </h4>
+              <p style={{ margin: '0 0 8px 0', fontSize: '13px', color: '#555' }}>
+                Data returned from local <code>fetchWeather</code> API:
+              </p>
+              <pre style={{ margin: 0, padding: '10px', backgroundColor: '#282c34', color: '#abb2bf', borderRadius: '4px', overflowX: 'auto', fontSize: '12px' }}>
+                {JSON.stringify(result.functionResult, null, 2)}
+              </pre>
+            </div>
+          )}
+
+          {/* Step 4 & 5: Final Synthesized Text Response */}
+          <div style={{ padding: '15px', border: '1px solid #ceebe1', borderRadius: '8px', backgroundColor: '#e6f4ea' }}>
+            <h4 style={{ margin: '0 0 8px 0', color: '#137333' }}>
+              Step 4 & 5: Final Model Response
+            </h4>
+            <p style={{ margin: 0, fontSize: '15px', color: '#202124', lineHeight: '1.5' }}>
+              {result.finalText}
+            </p>
+          </div>
+
+        </div>
+      )}
     </div>
   );
 }
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diff --git a/ai/ai-samples/src/features/function-calling/service.ts b/ai/ai-samples/src/features/function-calling/service.ts
index 6e9696125..50f0e7c08 100644
--- a/ai/ai-samples/src/features/function-calling/service.ts
+++ b/ai/ai-samples/src/features/function-calling/service.ts
@@ -1 +1,112 @@
-// Service for function-calling
\ No newline at end of file
+import { FunctionDeclarationsTool, Schema } from 'firebase/ai';
+import { getAiModel } from '../../services/firebaseAIService';
+
+export interface FunctionCallingResult {
+    functionCall?: {
+        name: string;
+        args: Record<string, any>;
+    };
+    functionResult?: Record<string, any>;
+    finalText: string;
+}
+
+/**
+ * Step 1: Write the local function.
+ * This interacts with your internal/external API or service.
+ */
+
+// This function calls a hypothetical external API that returns
+// a collection of weather information for a given location on a given date.
+// `location` is an object of the form { city: string, state: string }
+async function fetchWeather({ location, date }: { location: { city: string; state: string }; date: string }) {
+    // TODO(developer): Write a standard function that would call to an external weather API.
+    console.log(`Fetching mock weather for ${location.city}, ${location.state} on ${date}`);
+    // For demo purposes, this hypothetical response is hardcoded here in the expected format.
+    return {
+        temperature: 38,
+        chancePrecipitation: '56%',
+        cloudConditions: 'partlyCloudy',
+    };
+}
+
+/**
+ * Step 2: Create a function declaration.
+ * This defines the schema and description that Gemini uses to decide when to call the tool.
+ */
+const fetchWeatherTool: FunctionDeclarationsTool = {
+    functionDeclarations: [
+        {
+            name: 'fetchWeather',
+            description: 'Get the weather conditions for a specific city on a specific date',
+            parameters: Schema.object({
+                properties: {
+                    location: Schema.object({
+                        description: 'The name of the city and its state for which to get the weather. Only cities in the USA are supported.',
+                        properties: {
+                            city: Schema.string({ description: 'The city of the location.' }),
+                            state: Schema.string({ description: 'The US state of the location.' }),
+                        },
+                    }),
+                    date: Schema.string({
+                        description: 'The date for which to get the weather. Date must be in the format: YYYY-MM-DD.',
+                    }),
+                },
+            }),
+        },
+    ],
+};
+
+/**
+ * Steps 3-5: Execute the function calling round-trip.
+ */
+export async function executeFunctionCalling(prompt: string): Promise<FunctionCallingResult> {
+    // Step 3: Provide the function declaration during model initialization.
+    const model = getAiModel('gemini-3.6-flash', {
+        tools: [fetchWeatherTool],
+    });
+
+    const chat = model.startChat();
+
+    // Step 4: Call the function to invoke the external API.
+    // Send the user's question (the prompt) to the model using multi-turn chat.
+    let result = await chat.sendMessage(prompt);
+    const functionCalls = result.response.functionCalls() ?? [];
+
+    let functionCall: { name: string; args: Record<string, any> } | undefined;
+    let functionResult: Record<string, any> | undefined;
+    // When the model responds with one or more function calls, invoke the function(s).
+    if (functionCalls.length > 0) {
+        for (const call of functionCalls) {
+            if (call.name === 'fetchWeather') {
+                // Forward the structured input data prepared by the model
+                // to the hypothetical external API.
+                functionCall = { name: call.name, args: call.args as Record<string, any> };
+                functionResult = await fetchWeather(call.args as { location: { city: string; state: string }; date: string });
+            }
+        }
+    }
+
+    /**
+     * Step 5: Send the response from the function back to the model
+     * so that the model can use it to generate its final response.
+     */
+
+    if (functionCall && functionResult) {
+        result = await chat.sendMessage([
+            {
+                functionResponse: {
+                    name: functionCall.name, // "fetchWeather"
+                    response: functionResult,
+                },
+            },
+        ]);
+    }
+
+    const finalText = result.response.text();
+
+    return {
+        functionCall,
+        functionResult,
+        finalText,
+    };
+}
\ No newline at end of file