Filesystem MCP write_file returns success but files don't exist (Claude Desktop 1.1.8308, macOS)

[colorgreg]

Describe the bug
Filesystem MCP write_file tool returns success response but files are not created on disk. This affects all write operations to any directory, including allowed directories with Full Disk Access enabled.

To Reproduce
Steps to reproduce the behavior:

1. Configure Filesystem MCP with allowed directory: /Users/username
2. Enable Full Disk Access for Claude.app in macOS System Settings
3. Restart Claude Desktop (version 1.1.8308)
4. Call Filesystem:write_file with any path in allowed directory:

   Filesystem:write_file({
     path: "/Users/username/Desktop/test.txt",
     content: "test content"
   })

5. Tool returns success (no error)
6. Verify file existence: ls ~/Desktop/test.txt → No such file or directory

Expected behavior
File should be created at specified path when write_file returns success.

Logs
MCP logs from ~/Library/Logs/Claude/mcp-server-filesystem.log:

[Paste MCP logs here if available]

Additional context

• Environment: macOS (latest), Claude Desktop 1.1.8308 (updated March 19, 2026)
• MCP Config: Filesystem server configured, all tool permissions set to "Always allow"
• Full Disk Access: Enabled for Claude.app
• Tested locations: Home directory, Desktop, Documents - all fail
• Read operations: list_directory, read_file work correctly
• Write operations: All return success but no files created

This breaks all file delivery workflows - users cannot receive generated files.

Workarounds attempted (all failed):

• bash_tool with cp command
• Different directory locations
• Restart Claude Desktop
• Verify permissions

Issue started immediately after update to 1.1.8308.

[bryan-anthropic]

Thanks for the detailed report, @colorgreg.

A few questions to help us narrow this down:

1. Chat or Cowork? — Are you using this in a regular Claude Desktop chat conversation, or in Cowork (the agent/computer-use mode)? This is important because in Cowork, MCP servers run inside an isolated VM — writes succeed from the server's perspective but land on the VM filesystem rather than your host macOS filesystem. That would match the "success but no file" pattern you're describing.

2. Claude Desktop version — You mentioned this started with 1.1.8308 (March 19). Have you since updated to a newer version? If so, does the issue persist on the latest release?

3. MCP server logs — Could you share the contents of ~/Library/Logs/Claude/mcp-server-Filesystem.log? This will show us whether the write_file tool call is actually reaching the server and what the server responds with:

   cat ~/Library/Logs/Claude/mcp-server-Filesystem.log
   

4. Built-in Node.js setting — In Claude Desktop → Settings → Developer, is "Use built-in Node.js for MCP servers" enabled or disabled? This affects how the filesystem server process runs.

5. File location check — It's possible the file is being written to an unexpected path. Could you try running this in Terminal right after a write_file call:

   find ~/ -name "test.txt" -mmin -5 2>/dev/null
   

The server code uses standard Node.js fs.writeFile which either succeeds (file created) or throws an error (returned as a tool error). A silent success-but-no-file pattern would suggest something is intercepting or sandboxing the write at the environment level rather than a server-side issue.