[BUG] Claude Desktop Preview For Static HTML Pages Opens file:// Instead of Live Server — CSS Styles Not Loading

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Desktop automatically starts a Preview for HTML projects but then opens the preview using file://index.html protocol instead of pointing to the running HTTP server (http://localhost:PORT). This causes CSS stylesheets to fail loading silently, resulting in completely unstyled HTML rendering.

When I click "Preview" on an HTML file with external CSS stylesheets:

• Preview opens with URL: file://index.html
• CSS stylesheets fail to load completely
• Page renders completely unstyled (no colors, fonts, layouts, spacing)
• Images don't load
• No error messages shown

Same page renders perfectly in Chrome on http://localhost:PORT or via fille://{fullpath}

What Should Happen?

Claude Desktop should open the preview to the live server it started (http://localhost:PORT), not file://.
also no issues if it opens it with fille://{fullpath} if that will show the correct page with styles

Steps:

1. Claude Desktop starts live server on http://localhost:XXXX
2. Preview opens to http://localhost:XXXX (or http://localhost:XXXX/index.html)
3. All CSS, images, and JavaScript load correctly
4. Page renders exactly as it appears in Chrome on localhost

This is a routing issue—the server plumbing exists, but the wrong endpoint is being used.

Error Messages/Logs

None

Steps to Reproduce

1. Open Claude Desktop
2. Create or open an HTML project with external CSS files:

• Create index.html with a link to an external stylesheet:

<link rel="stylesheet" href="./styles.css">

• Create styles.css with basic styling:

body { background-color: blue; color: white; font-size: 18px; }
h1 { margin: 20px; }

1. In Claude Desktop, click "Preview" on the index.html file
2. Observe the preview panel opens with URL: file://index.html
3. Notice: CSS is NOT applied—page shows unstyled plain HTML

• No background color
• No custom fonts or colors
• No spacing or layout styling
• Just raw browser defaults

Expected: Preview should open to http://localhost:PORT and CSS should load correctly
Actual: Preview opens to file:// protocol and CSS fails silently

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

1.15962.0 (039543)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_