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[BUG] Filesystem MCP server (remote-devices) fails all tool calls: outputSchema declares unsupported draft-07 dialect #88988
Description
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?
Every tool call to the filesystem MCP server (accessed via the remote-devices bridge in Cowork mode) fails immediately with a schema validation error, regardless of which tool is called. Tested with list_allowed_directories, list_directory, read_text_file, and write_file — all fail identically.
What Should Happen?
The filesystem tools should execute normally and return directory listings / file contents, as they did before 2026-08-22. The tool's outputSchema should validate correctly against the client's JSON Schema validator instead of failing before the call even reaches the server logic.
Error Messages/Logs
Error: Tool '<toolname>' has an invalid outputSchema: JSON Schema declares an unsupported dialect ("$schema": "http://json-schema.org/draft-07/schema#"). The default validator supports JSON Schema 2020-12 only; pass a pre-configured Ajv instance to AjvJsSteps to Reproduce
- Open Claude (Cowork mode) on Windows 11 with a connected folder/network drive (P:)
- Call any filesystem MCP tool, e.g. list_allowed_directories or list_directory
- Observe the tool call fails immediately with the outputSchema error above
- Repeat with other filesystem tools (read_text_file, write_file, etc.) — same error every time
Claude Model
Sonnet (default)
Is this a regression?
Yes, this worked in a previous version
Last Working Version
No response
Claude Code Version
N/A — using Claude (Cowork mode) via the Claude Desktop app, not the Claude Code CLI.
Platform
Anthropic API
Operating System
Windows
Terminal/Shell
Windows Terminal
Additional Information
Reported to Anthropic support first; support confirmed this looks like a server-side draft-07 vs. 2020-12 schema mismatch and suggested filing here since it wasn't resolvable via client config or restart.
Related but not identical issues:
- [BUG] Claude Desktop macOS: filesystem MCP server unusable in both package generations - new schema never dispatched, old schema dropped at registration #80094 (macOS, different symptom — outputSchema/structuredContent dispatch failure)
- [BUG] Claude Desktop filesystem MCP — tool calls fail with empty server logs despite server running normally #80252 (Windows, similar filesystem connector setup, but empty logs / no schema error mentioned)
Blocks a recurring automated task reading/writing files on a connected network drive (P:).
Activity
MatejKral commentedon Aug 28, 2026
Confirming — hitting this exact issue too.
Environment
What I see
Every tool on this extension fails with the identical error, both read-only and write:
Confirmed on: list_directory, list_directory_with_sizes, directory_tree, list_allowed_directories, move_file.
Already tried, none of it helped
Same error every time, so this doesn't look like a stale-connection or permission problem — looks like the app's bundled Ajv validator genuinely can't validate this server's draft-07 outputSchema, exactly as described in the issue title. This makes the extension a complete outage for me, not a partial one — no read or write operations work at all.
bug_report.md
localden commentedon Oct 11, 2026
Duplicate of #87633. We'll be consolidating the discussion there.