MCP tool output schemas declare `draft-07` dialect — rejected by clients enforcing JSON Schema 2020-12

[seasonsbrick-cell]

What happened?

Every tool call against the local @pascal-app/mcp server fails immediately with a schema validation error, even though the server process itself starts and runs fine:

Error: Tool '<tool_name>' 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 AjvJs

Confirmed to affect every tool tried, including: list_levels, get_walls, export_json, create_project, list_scenes.

Environment:

• Package: @pascal-app/mcp (installed via bunx @pascal-app/mcp, unpinned/latest tag as of 2026-08-20)
• Client: Claude Desktop (macOS), via its MCP connector config
• The server itself starts fine standalone (bunx @pascal-app/mcp prints "[pascal-mcp] stdio server running" and hangs waiting for a client) — so this is specifically about how tool output schemas are declared, not a startup/connectivity issue.
• Refreshing the client's tool list and fully restarting the MCP connection does not change the error.

Steps to reproduce

1. Configure @pascal-app/mcp as an MCP server in Claude Desktop (bunx @pascal-app/mcp)
2. Call any tool, e.g. list_levels, get_walls, or export_json
3. See the outputSchema validation error above instead of a result

Expected behavior

The tool call should succeed and return the requested data. The outputSchema fields should use the JSON Schema 2020-12 dialect (or omit/correctly declare $schema) so MCP clients with strict validators (like Claude Desktop's) can validate the response.

Browser & OS

macOS (Claude Desktop), Node/bun runtime via bunx @pascal-app/mcp

Screenshots or screen recordings

No response

Additional context

No response