[BUG]

[phlaster]

Bug Description

The write_note, read_note, canvas, search_notes, and recent_activity tools in basic-memory MCP consistently fail Pydantic validation when invoked by a local LLM (qwen3.6-27b, quite capable in toolcalling in other situations). Input payloads contain malformed structures with unexpected keys like : [, [{, or fragmented JSON, suggesting a mismatch between the exposed MCP schema and the Pydantic validator.

Steps To Reproduce

1. Install via uv: uvx basic-memory
2. Configure MCP client to connect to the server
3. Prompt the model to use any memory tool with standard parameters
4. Observe ValidationError exceptions in server logs

Expected Behavior

Model generates valid tool calls matching Pydantic schemas; server accepts and processes them successfully.

Actual Behavior

Repeated validation failures across all tested tools. Representative error:

ValidationError: 3 validation errors for call[write_note]
title
  Missing required argument [type=missing_argument, input_value={'content': '...', ': [': [{}, '[{']}, input_type=dict]
: [
  Unexpected keyword argument [type=unexpected_keyword_argument, input_value=[{}, '[{'], input_type=list]

Key pattern: legitimate parameter values appear assigned to garbage keys (: [, [{), while required fields are reported missing. Failures are non-deterministic.

Environment

• OS: CachyOS (Arch derivative)
• Python: 3.13 | Basic Memory: 0.20.3 | uv: 0.11.10
• LLM: Jackrong/Qwopus3.6-27B-v1-preview-Q4_K_M (LMStudio)
• MCP client: standard mcp Python library

Additional Context

• Issue persists across tools and prompts; no custom config used
• Same model works with other MCP servers having simpler schemas
• Error pattern suggests schema serialization or LLM interpretation issue, not model capability

Possible Solution

1. Audit JSON Schema exposure via tools/list for ambiguity or mismatch with Pydantic models
2. Add pre-validation logging to capture raw payloads before Pydantic processing
3. Simplify tool schemas: flatten nested params, clarify field descriptions, avoid complex unions
4. Consider lenient pre-processing to filter unknown keys before validation

[phernandez]

Hi @phlaster pretty sure this is the models fault. but can you include some logs so we can look at the requests?

[phlaster]

Hi @phlaster pretty sure this is the models fault. but can you include some logs so we can look at the requests?

Hi, thx for your quick response. I've just been testing your tool with Jackrong/Qwopus3.6-35B-A3B-v1-Q5_K_M and this time all requests were fine, so I guess it's some generation parameters quirk or something else on my side...

Anyway, it looked like this in my console log:

[05/06/26 22:27:12] Error validating tool 'write_note'                            
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 3 validation errors for call[write_note]     
                    content                                                       
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'my content...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    directory                                                     
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'Состоян...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    : []}}}]}]}}], [{}]: {}}, [{]]}: {                            
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    Error validating tool 'write_note'                            
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 3 validation errors for call[write_note]     
                    content                                                       
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'Состоян...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    directory                                                     
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'Состоян...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    : []}}}]}]}}], [{}]: {}}, [{]]}: {                            
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                    
[05/06/26 22:41:19] Error validating tool 'write_note'                            
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 3 validation errors for call[write_note]     
                    content                                                       
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'my content...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    directory                                                     
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'my content...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    : []}}]}]}}], [{}]: {}}, [{]]}: {                             
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    Error validating tool 'write_note'                            
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 3 validation errors for call[write_note]     
                    content                                                       
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'my content...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    directory                                                     
                      Missing required argument [type=missing_argument,           
                    input_value={'title': 'my content...[{}]: {}}, [{]]}: {': 1},    
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    : []}}]}]}}], [{}]: {}}, [{]]}: {                             
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
[05/06/26 22:46:50] Error validating tool 'write_note'                            
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 2 validation errors for call[write_note]     
                    directory                                                     
                      Missing required argument [type=missing_argument,           
                    input_value={'content': 'my content'},           
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    : {}, [{}: {}]}}], [{                                         
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    Error validating tool 'write_note'                            
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 2 validation errors for call[write_note]     
                    directory                                                     
                      Missing required argument [type=missing_argument,           
                    input_value={'content': 'my content'},           
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/missing_argument           
                    : {}, [{}: {}]}}], [{                                         
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
...
[05/06/26 23:15:26] Error validating tool 'search_notes'                          
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 1 validation error for call[search_notes]    
                    : []}}]}]}}], [{}]: {}}, [{]]}: {                             
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    Error validating tool 'search_notes'                          
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 1 validation error for call[search_notes]    
                    : []}}]}]}}], [{}]: {}}, [{]]}: {                             
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=1,             
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
[05/06/26 23:15:38] Error validating tool 'recent_activity'                       
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 5 validation errors for call[recent_activity]
                    : 3}}]}}]}: []}, [{]]}: {                                     
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=10,            
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    : [{}]: [                                                     
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value='',            
                    input_type=str]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                                                                                  
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value='entity',      
                    input_type=str]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    :                                                             
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value={},            
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    [{[{}], {}]: [], }]                                           
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value='note',        
                    input_type=str]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    Error validating tool 'recent_activity'                       
                    ╭──────────── Traceback (most recent call last) ─────────────╮
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/server/server.py:1240 in          │
                    │ call_tool                                                  │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/base.py:377 in _run         │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/fastmcp/tools/function_tool.py:278 in run │
                    │                                                            │
                    │ /home/user/.local/share/uv/tools/basic-memory/lib/python3. │
                    │ 13/site-packages/pydantic/type_adapter.py:441 in           │
                    │ validate_python                                            │
                    ╰────────────────────────────────────────────────────────────╯
                    ValidationError: 5 validation errors for call[recent_activity]
                    : 3}}]}}]}: []}, [{]]}: {                                     
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value=10,            
                    input_type=int]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    : [{}]: [                                                     
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value='',            
                    input_type=str]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                                                                                  
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value='entity',      
                    input_type=str]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    :                                                             
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value={},            
                    input_type=dict]                                              
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument
                    [{[{}], {}]: [], }]                                           
                      Unexpected keyword argument                                 
                    [type=unexpected_keyword_argument, input_value='note',        
                    input_type=str]                                               
                        For further information visit                             
                    https://errors.pydantic.dev/2.13/v/unexpected_keyword_argument

All these unexpected_keyword_argument and missing_argument made me think that it possibly was an issue with the tool annotations.