"MCP Server: question_graphs tool fails silently - parameter serialization issue"

[jpunishill]

MCP server version: 2.3.2 (writer-sdk-mcp@latest)
Working tools: list_graphs, retrieve_graphs, list_applications
Failing tool: question_graphs
Error: "Tool execution failed" with no details
Suspected cause: graph_ids array not being serialized correctly
Direct curl to API works (if confirmed in Step 1)

[jpunishill]

Writer MCP Server - Two Tools Failing Despite Write Permissions

Environment

• Platform: Claude.ai web interface
• MCP Server: Writer (official, writer-sdk-mcp)
• Graph ID: 376d48dd-6378-484e-934c-3144c2e5afb5
• Permissions: Read AND Write both enabled in MCP configuration
• Test Date: December 10, 2025

Executive Summary

After enabling Write permissions in MCP configuration, 9 of 11 tested Writer MCP tools now work correctly. However, writer:upload_files and writer:question_graphs continue to fail with generic error messages despite documentation indicating these features should be supported.

✅ Working Tools (9/11)

All graph and file management operations work correctly:

• writer:list_graphs - List all Knowledge Graphs
• writer:retrieve_graphs - Get graph details by ID
• writer:create_graphs - Create new Knowledge Graph
• writer:update_graphs - Update graph metadata
• writer:delete_graphs - Delete Knowledge Graph
• writer:list_files - List files with filters/pagination
• writer:retrieve_files - Get file metadata by ID
• writer:add_file_to_graph_graphs - Associate file with graph
• writer:remove_file_from_graph_graphs - Remove file from graph

❌ Failing Tools (2/11)

1. writer:upload_files

Error: "Tool execution failed"

Test Case:

{
  "Content-Disposition": "attachment; filename=\"MCP_TEST.md\"",
  "content": "# Test File\n**Date:** December 10, 2025\n..."
}

Expected: File uploaded, file_id returned
Actual: Generic failure with no diagnostic information

Documentation Reference: MCP Server docs state the server can "Upload and analyze files"

Workaround Available: Direct API call succeeds:

curl -X POST 'https://api.writer.com/v1/files' \
  -H "Authorization: Bearer $API_KEY" \
  -H 'Content-Type: text/plain' \
  -H 'Content-Disposition: attachment; filename="test.md"' \
  --data-binary "@file.md"

---

2. writer:question_graphs

Error: "Tool execution failed"

Test Case:

{
  "graph_ids": ["376d48dd-6378-484e-934c-3144c2e5afb5"],
  "question": "What is the DAVE checkpoint system?",
  "stream": false
}

Expected: Answer generated from Knowledge Graph content
Actual: Generic failure with no diagnostic information

Documentation Reference: MCP Server docs state the server can "Query Knowledge Graphs for research"

Notes:

• Graph contains 60 completed, successfully processed files
• All READ operations (retrieve_graphs, list_files) confirm files are accessible
• No API workaround available for Knowledge Graph queries

---

Impact

Priority: Medium

Current State:

• 82% of Writer MCP functionality works with proper permissions
• File upload has workaround (direct API)
• Knowledge Graph querying unavailable (no workaround)
• Generic error messages prevent debugging

User Impact:

• MCP integration incomplete for documented workflows
• Users must maintain separate API scripts for uploads
• Knowledge Graph query feature (core MCP value prop) unusable

---

Reproduction Steps

1. Configure Writer MCP with valid API key and Write permissions enabled
2. Verify READ operations work: writer:list_graphs, writer:list_files
3. Attempt WRITE operation: writer:upload_files with test content
4. Observe: "Tool execution failed" with no additional context
5. Attempt QUERY operation: writer:question_graphs with valid graph_id
6. Observe: "Tool execution failed" with no additional context
7. Compare: Same upload operation via direct API succeeds

---

Expected Resolution

Ideal: Both upload_files and question_graphs work through MCP matching documented capabilities

Minimum: Clear error messages indicating specific failure reason (permissions, rate limits, invalid parameters, network issues, etc.) instead of generic "Tool execution failed"

---

Additional Context

Initial debugging note: Earlier testing showed all operations failing due to incorrect Graph ID in user configuration (434e vs 484e). After correction, 9 tools began working, confirming credentials and permissions are valid.

Available for follow-up: Can provide additional diagnostic information or testing as needed.