[BUG] [Claude Desktop / macOS] Registers as default handler for .md without consent (not claude-cli://)

Preflight Checklist

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

What's Wrong?

Routing note

This is Claude Desktop on macOS, not Claude Code CLI/VS Code. Filing here because Desktop has no public issue tracker. Same precedent as #93011 and other Desktop reports that bots close as "invalid."

What's wrong

Claude Desktop silently becomes the macOS default app for Markdown (.md / net.daringfireball.markdown) via Launch Services. No consent prompt. Mail attachments and Finder opens go to Claude instead of the user's prior default (e.g. TextEdit).

Support's documented fix (disableDeepLinkRegistration for claude-cli://) does not address file-type associations.

Expected

• No change to OS default apps without explicit user opt-in
• Or a clear Desktop setting: "Do not register as default handler for file types"

Actual

• .md default became Claude Desktop (com.anthropic.claudefordesktop)
• Required manual Launch Services repair to restore TextEdit
• Forcing Preview for .md failed (Preview does not reliably open Markdown)

Environment

• Claude Desktop (Mac) version 2.2553.1
• macOS 26.6.2 (Build 25G83)
• Repro: install/use Desktop → open .md from Mail/Finder → opens in Claude

Related

• #93011 (Windows Desktop reclaiming defaults on every launch; closed as not Claude Code)
• #91750 (Windows Desktop registering as default for .docx/.pdf/.csv)

Requested fix

Gate all default-app / document-type registration behind a persisted opt-in. Document a Desktop setting distinct from protocol deep-link registration.

What Should Happen?

Claude Desktop should not change macOS default apps without an explicit user opt-in.

Specifically:

• Installing or launching Claude Desktop must not set Claude as the default handler for Markdown (.md) or other document types.
• Mail attachments and Finder double-clicks should continue to open in the user's existing default app (e.g. TextEdit for .md).
• If Claude wants to offer “Open with Claude,” that should be an Open With choice or an in-app action — not a silent Launch Services default.
• Ideally, Desktop Settings should include a clear toggle such as “Do not register as default handler for file types,” separate from any claude-cli:// / deep-link setting.

Error Messages/Logs

None — no error dialog was shown.

The failure mode was silent: Claude Desktop became the macOS default app for .md without a prompt or error. Mail/Finder then opened Markdown in Claude instead of TextEdit.

Optional diagnostics (if useful to the team):
- `mdls -name kMDItemContentType` on a .md file
- Launch Services default handler for `net.daringfireball.markdown` pointed at Claude Desktop (`com.anthropic.claudefordesktop`) before repair
- Claude Desktop version: 2.2553.1
- macOS: 26.6.2 (Build 25G83)

Steps to Reproduce

1. On macOS, note the current default app for Markdown (.md), e.g. TextEdit (Get Info → Open with, or open a .md from Finder).
2. Install or launch Claude Desktop (Mac app). Use it normally (no explicit “make default” action).
3. Quit and reopen Mail or Finder if needed.
4. Double-click a .md file in Finder, or open a .md email attachment.
5. Observe which app opens.

Expected: still opens in the prior default (e.g. TextEdit).
Actual: opens in Claude Desktop; Claude is now the Launch Services default for .md / net.daringfireball.markdown.

Also observed: Claude Desktop Info.plist claims broad document/viewer types including All Files / public.data, which facilitates claiming defaults without a user prompt.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

Claude Desktop APP

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Additional information

There is currently no supported Claude Desktop setting to stop this.

• Anthropic support pointed to disableDeepLinkRegistration / claude-cli://. That only covers a URL protocol handler. It does not stop Desktop from claiming OS file-type defaults for .md.
• The only workaround we found is a manual macOS Launch Services repair (terminal / defaults database) to point Markdown back to TextEdit.
• That repair does not stick as a product fix: after Claude Desktop is opened again (and/or after updates), the association can be reclaimed and .md / Mail attachments open in Claude again until the manual repair is repeated.
• Related: #93011 (Windows) reports Desktop reclaiming file-type defaults on every launch, with no in-app opt-out. #91750 is similar for other document types on Windows.
• Requested product fix: a persisted Desktop opt-out for file-type / default-app registration, separate from deep-link settings, defaulting to off (do not claim defaults without consent).

The report concerns Claude Desktop on macOS rather than Claude Code, and names no repository file, test, or code entry point. Start by confirming product ownership and reproducing the Launch Services association with the listed macOS steps; done would mean a persisted opt-in prevents unsolicited .md/default-handler registration.