diff --git a/jam-ui/test/chat/send-message.spec.ts b/jam-ui/test/chat/send-message.spec.ts
new file mode 100644
index 000000000..7a293906a
--- /dev/null
+++ b/jam-ui/test/chat/send-message.spec.ts
@@ -0,0 +1,167 @@
+import { test, expect } from '@playwright/test';
+import { loginToJamUI, createAndJoinSession } from '../utils/test-helpers';
+
+test.describe('Send Message', () => {
+  test.beforeEach(async ({ page }) => {
+    await loginToJamUI(page);
+    await createAndJoinSession(page);
+
+    // Open chat window
+    const chatButton = page.locator('img[alt="Chat"]');
+    await chatButton.click();
+  });
+
+  test('sends message when Send button clicked', async ({ page, context }) => {
+    // Wait for popup
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    // Type message
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    await textarea.fill('Hello from test!');
+
+    // Click send button
+    const sendButton = popup.locator('button:has-text("Send")');
+    await sendButton.click();
+
+    // Wait for message to appear in list
+    await popup.waitForTimeout(500);
+    const message = popup.locator('text=Hello from test!');
+    await expect(message).toBeVisible();
+
+    // Verify textarea cleared
+    await expect(textarea).toHaveValue('');
+  });
+
+  test('sends message when Enter key pressed', async ({ page, context }) => {
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    await textarea.fill('Hello via Enter!');
+
+    // Press Enter (not Shift+Enter)
+    await textarea.press('Enter');
+
+    // Message should appear
+    await popup.waitForTimeout(500);
+    const message = popup.locator('text=Hello via Enter!');
+    await expect(message).toBeVisible();
+
+    // Textarea cleared
+    await expect(textarea).toHaveValue('');
+  });
+
+  test('inserts newline when Shift+Enter pressed', async ({ page, context }) => {
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    await textarea.fill('Line 1');
+
+    // Press Shift+Enter
+    await textarea.press('Shift+Enter');
+
+    // Type second line
+    await textarea.type('Line 2');
+
+    // Verify multiline content
+    const value = await textarea.inputValue();
+    expect(value).toContain('\n');
+    expect(value).toContain('Line 1');
+    expect(value).toContain('Line 2');
+
+    // Message NOT sent yet
+    const messages = popup.locator('[data-testid="chat-message"]');
+    expect(await messages.count()).toBe(0);
+  });
+
+  test('disables send button when message empty', async ({ page, context }) => {
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    const sendButton = popup.locator('button:has-text("Send")');
+
+    // Initially disabled (empty)
+    await expect(sendButton).toBeDisabled();
+
+    // Type message - becomes enabled
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    await textarea.fill('Test message');
+    await expect(sendButton).toBeEnabled();
+
+    // Clear - becomes disabled again
+    await textarea.fill('');
+    await expect(sendButton).toBeDisabled();
+  });
+
+  test('disables send button when message over 255 characters', async ({ page, context }) => {
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    const sendButton = popup.locator('button:has-text("Send")');
+
+    // Type 256 characters
+    const longMessage = 'a'.repeat(256);
+    await textarea.fill(longMessage);
+
+    // Send button disabled
+    await expect(sendButton).toBeDisabled();
+
+    // Character count shows red and over-limit
+    const charCount = popup.locator('text=/256\\/255/');
+    await expect(charCount).toBeVisible();
+
+    // Validation message appears
+    const validationMsg = popup.locator('text=/characters too long/i');
+    await expect(validationMsg).toBeVisible();
+  });
+
+  test('shows error when send fails', async ({ page, context }) => {
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    // Simulate send failure by mocking the API to fail
+    await page.route('**/api/chat/messages', route => {
+      route.fulfill({
+        status: 500,
+        body: JSON.stringify({ error: 'Internal server error' })
+      });
+    });
+
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    await textarea.fill('Test failure');
+
+    const sendButton = popup.locator('button:has-text("Send")');
+    await sendButton.click();
+
+    // Error message should appear
+    await popup.waitForTimeout(500);
+    const errorMsg = popup.locator('text=/Failed to send message/i');
+    await expect(errorMsg).toBeVisible();
+  });
+
+  test('shows optimistic update immediately', async ({ page, context }) => {
+    const popupPromise = context.waitForEvent('page');
+    const popup = await popupPromise;
+    await popup.waitForLoadState('domcontentloaded');
+
+    const textarea = popup.locator('textarea[placeholder*="Type a message"]');
+    await textarea.fill('Optimistic test');
+
+    const sendButton = popup.locator('button:has-text("Send")');
+    await sendButton.click();
+
+    // Message should appear immediately (optimistic)
+    // Don't wait for server - should show right away
+    const message = popup.locator('text=Optimistic test');
+    await expect(message).toBeVisible({ timeout: 1000 });
+  });
+});