Memory MCP Server

A Model Context Protocol (MCP) server that provides knowledge graph functionality for managing entities, relations, and observations in memory, with strict validation rules to maintain data consistency.

Installation

Install the server in Claude Desktop:

mcp install main.py -v MEMORY_FILE_PATH=/path/to/memory.jsonl

Data Validation Rules

Entity Names

• Must start with a lowercase letter
• Can contain lowercase letters, numbers, and hyphens
• Maximum length of 100 characters
• Must be unique within the graph
• Example valid names: python-project, meeting-notes-2024, user-john

Entity Types

The following entity types are supported:

• person: Human entities
• concept: Abstract ideas or principles
• project: Work initiatives or tasks
• document: Any form of documentation
• tool: Software tools or utilities
• organization: Companies or groups
• location: Physical or virtual places
• event: Time-bound occurrences

Observations

• Non-empty strings
• Maximum length of 500 characters
• Must be unique per entity
• Should be factual and objective statements
• Include timestamp when relevant

Relations

The following relation types are supported:

• knows: Person to person connection
• contains: Parent/child relationship
• uses: Entity utilizing another entity
• created: Authorship/creation relationship
• belongs-to: Membership/ownership
• depends-on: Dependency relationship
• related-to: Generic relationship

Additional relation rules:

• Both source and target entities must exist
• Self-referential relations not allowed
• No circular dependencies allowed
• Must use predefined relation types

Usage

The server provides tools for managing a knowledge graph:

Get Entity

result = await session.call_tool("get_entity", {
    "entity_name": "example"
})
if not result.success:
    if result.error_type == "NOT_FOUND":
        print(f"Entity not found: {result.error}")
    elif result.error_type == "VALIDATION_ERROR":
        print(f"Invalid input: {result.error}")
    else:
        print(f"Error: {result.error}")
else:
    entity = result.data
    print(f"Found entity: {entity}")

Get Graph

result = await session.call_tool("get_graph", {})
if result.success:
    graph = result.data
    print(f"Graph data: {graph}")
else:
    print(f"Error retrieving graph: {result.error}")

Create Entities

# Valid entity creation
entities = [
    Entity(
        name="python-project",  # Lowercase with hyphens
        entityType="project",   # Must be a valid type
        observations=["Started development on 2024-01-29"]
    ),
    Entity(
        name="john-doe",
        entityType="person",
        observations=["Software engineer", "Joined team in 2024"]
    )
]
result = await session.call_tool("create_entities", {
    "entities": entities
})
if not result.success:
    if result.error_type == "VALIDATION_ERROR":
        print(f"Invalid entity data: {result.error}")
    else:
        print(f"Error creating entities: {result.error}")

Add Observation

# Valid observation
result = await session.call_tool("add_observation", {
    "entity": "python-project",
    "observation": "Completed initial prototype"  # Must be unique for entity
})
if not result.success:
    if result.error_type == "NOT_FOUND":
        print(f"Entity not found: {result.error}")
    elif result.error_type == "VALIDATION_ERROR":
        print(f"Invalid observation: {result.error}")
    else:
        print(f"Error adding observation: {result.error}")

Create Relation

# Valid relation
result = await session.call_tool("create_relation", {
    "from_entity": "john-doe",
    "to_entity": "python-project",
    "relation_type": "created"  # Must be a valid type
})
if not result.success:
    if result.error_type == "NOT_FOUND":
        print(f"Entity not found: {result.error}")
    elif result.error_type == "VALIDATION_ERROR":
        print(f"Invalid relation data: {result.error}")
    else:
        print(f"Error creating relation: {result.error}")

Search Memory

result = await session.call_tool("search_memory", {
    "query": "most recent workout"  # Supports natural language queries
})
if result.success:
    if result.error_type == "NO_RESULTS":
        print(f"No results found: {result.error}")
    else:
        results = result.data
        print(f"Search results: {results}")
else:
    print(f"Error searching memory: {result.error}")

The search functionality supports:

• Temporal queries (e.g., “most recent”, “last”, “latest”)
• Activity queries (e.g., “workout”, “exercise”)
• General entity searches
• Fuzzy matching with 80% similarity threshold
• Weighted search across:
  • Entity names (weight: 1.0)
  • Entity types (weight: 0.8)
  • Observations (weight: 0.6)

Delete Entities

result = await session.call_tool("delete_entities", {
    "names": ["python-project", "john-doe"]
})
if not result.success:
    if result.error_type == "NOT_FOUND":
        print(f"Entity not found: {result.error}")
    else:
        print(f"Error deleting entities: {result.error}")

Delete Relation

result = await session.call_tool("delete_relation", {
    "from_entity": "john-doe",
    "to_entity": "python-project"
})
if not result.success:
    if result.error_type == "NOT_FOUND":
        print(f"Entity not found: {result.error}")
    else:
        print(f"Error deleting relation: {result.error}")

Flush Memory

result = await session.call_tool("flush_memory", {})
if not result.success:
    print(f"Error flushing memory: {result.error}")

Error Types

The server uses the following error types:

• NOT_FOUND: Entity or resource not found
• VALIDATION_ERROR: Invalid input data
• INTERNAL_ERROR: Server-side error
• ALREADY_EXISTS: Resource already exists
• INVALID_RELATION: Invalid relation between entities

Response Models

All tools return typed responses using these models:

EntityResponse

class EntityResponse(BaseModel):
    success: bool
    data: Optional[Dict[str, Any]] = None
    error: Optional[str] = None
    error_type: Optional[str] = None

GraphResponse

class GraphResponse(BaseModel):
    success: bool
    data: Optional[Dict[str, Any]] = None
    error: Optional[str] = None
    error_type: Optional[str] = None

OperationResponse

class OperationResponse(BaseModel):
    success: bool
    error: Optional[str] = None
    error_type: Optional[str] = None

Development

Running Tests

pytest tests/

Adding New Features

1. Update validation rules in validation.py
2. Add tests in tests/test_validation.py
3. Implement changes in knowledge_graph_manager.py