Memory MCP JSON Parsing Error - All Tools Failing

[FranzKiller]

Describe the bug

All Memory MCP tools fail with the same JSON parsing error: Unexpected non-whitespace character after JSON at position 175 (line 1 column 176). This occurs even for simple read operations like read_graph, search_nodes, and open_nodes.

To Reproduce

Steps to reproduce the behavior:

1. Configure Memory Tool MCP server in ~/.cursor/mcp.json:n
   "Memory Tool": {
   "command": "cmd",
   "args": [
   "/c",
   "npx",
   "-y",
   "@modelcontextprotocol/server-memory"
   ]
   }
   2. Restart Cursor IDE to load the MCP server

2. Attempt to use any Memory Tool MCP function:

   • read_graph() - fails with JSON parsing error
   • search_nodes("query") - fails with JSON parsing error
   • open_nodes(["entity"]) - fails with JSON parsing error
   • create_entities(...) - fails with JSON parsing error

3. All tools return the same error: Unexpected non-whitespace character after JSON at position 175 (line 1 column 176)

Expected behavior

Memory Tool MCP tools should work correctly, especially read operations like read_graph which should return an empty graph if no data exists.

Environment

• Server Version: @modelcontextprotocol/server-memory@2025.11.25 (latest)
• IDE: Cursor IDE (Windows)
• OS: Windows 10.0.22631
• Node.js: (via npx)
• Data Directory: C:\Users\Franc\.cursor\projects\c-ProgettiIscobol-sn22\mcps\user-Memory_Tool (empty - no existing data)

Logs

All tool calls return:
Restart Cursor IDE to load the MCP server
Attempt to use any Memory Tool MCP function:
read_graph() - fails with JSON parsing error
search_nodes("query") - fails with JSON parsing error
open_nodes(["entity"]) - fails with JSON parsing error
create_entities(...) - fails with JSON parsing error
All tools return the same error: Unexpected non-whitespace character after JSON at position 175 (line 1 column 176)
Expected behavior
Memory Tool MCP tools should work correctly, especially read operations like read_graph which should return an empty graph if no data exists.
Environment
Server Version: @modelcontextprotocol/server-memory@2025.11.25 (latest)
IDE: Cursor IDE (Windows)
OS: Windows 10.0.22631
Node.js: (via npx)
Data Directory: C:\Users\Franc.cursor\projects\c-ProgettiIscobol-sn22\mcps\user-Memory_Tool (empty - no existing data)
Logs
All tool calls return:
Error: Unexpected non-whitespace character after JSON at position 175 (line 1 columnsonl file exists)- Using the simplest possible operations (read_graphwith no parameters)- The server version is the latest available (2025.11.25)## Additional context- The error position (175) suggests the server is returning a malformed JSON response- The problem occurs even with an empty knowledge graph (no existing data)- All tools fail with the same error, suggesting a systemic issue rather than data corruption- The server starts correctly (no startup errors)- The MCP connection is established (tools are recognized)## Related Issues- #3144 - Schema Validation Error (different issue, related to additional properties)- #3137 -open_nodes` returns empty relations (different issue, related to relations)## Suggested Solutions1. Investigate JSON serialization: The error suggests the server is generating malformed JSON responses2. Check empty state handling: The error occurs even with no data, suggesting the server may not handle empty graphs correctly3. Verify MCP protocol compliance: Ensure the server's JSON responses comply with MCP protocol specifications
This error occurs even when:
The data directory is completely empty (no memory.jsonl file exists)
Using the simplest possible operations (read_graph with no parameters)
The server version is the latest available (2025.11.25)
Additional context
The error position (175) suggests the server is returning a malformed JSON response
The problem occurs even with an empty knowledge graph (no existing data)
All tools fail with the same error, suggesting a systemic issue rather than data corruption
The server starts correctly (no startup errors)
The MCP connection is established (tools are recognized)
Related Issues
#3144 - Schema Validation Error (different issue, related to additional properties)
#3137 - open_nodes returns empty relations (different issue, related to relations)
Suggested Solutions
Investigate JSON serialization: The error suggests the server is generating malformed JSON responses
Check empty state handling: The error occurs even with no data, suggesting the server may not handle empty graphs correctly
Verify MCP protocol compliance: Ensure the server's JSON responses comply with MCP protocol specifications
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