mimory-mcp-focus

A focus-enforcing wrapper for MCP (Model Context Protocol) Python clients that provides fine-grained control over tool access and parameter validation through allowlists and JWT-based context extraction.

Features

• Tool Filtering: Restrict access to specific MCP tools
• Parameter Focusing: Enforce allowed values for tool parameters, only handles exact matches, ranges, and * wildcards
• JWT Integration: Extract focus context from JWT tokens
• Flexible Configuration: Support for both simple and composite focus configurations
• Range Focusing: Support for numeric range constraints
• Strict Mode: Optional strict parameter validation that requires all passed parameters be included in the focus_params

Future Work

• Full MCP Coverage: Focus all MCP features including resources, prompts, and more
• Improved Focusing: Better pattern matching for focus enforcement
• Easier JWT Integration: Signed JWTs, even when not used as access tokens, should automatically update the context

Installation

pip install mimory-mcp-focus

Quick Start

Basic Usage with Simple Focus

import asyncio
from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client
from mimory_mcp_focus import focus_client_simple

async def main():
    # Create MCP server parameters
    server_params = StdioServerParameters(
        command="npx",
        args=["-y", "@modelcontextprotocol/server-everything"]
    )
    
    # Connect to MCP server
    async with stdio_client(server_params) as (read, write):
        async with ClientSession(read, write) as session:
            # Create focused client with restrictions
            focus_client = focus_client_simple(
                session=session,
                focus_tools=["echo", "add"],  # Only allow these tools
                focus_params={
                    "message": ["hello", "world"],  # Only allow these messages
                    "a": ["1", "2", "3"],          # Only allow these values for 'a'
                    "b": ["range:1-10"]            # Allow any number between 1-10
                },
                strict=True  # Require all parameters to be in focus_params
            )
            
            # List available tools (filtered)
            tools = await focus_client.list_tools()
            print(f"Available tools: {[tool.name for tool in tools.tools]}")
            
            # Call allowed tool with valid parameters
            result = await focus_client.call_tool("echo", {"message": "hello"})
            print(f"Echo result: {result.content}")

if __name__ == "__main__":
    asyncio.run(main())

Using Composite Focus

import asyncio
from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client
from mimory_mcp_focus import focus_client_composite

async def main():
    server_params = StdioServerParameters(
        command="npx",
        args=["-y", "@modelcontextprotocol/server-everything"]
    )
    
    async with stdio_client(server_params) as (read, write):
        async with ClientSession(read, write) as session:
            # Create composite focus client
            focus_client = focus_client_composite(
                session=session,
                focus={
                    "echo": {  # Specific rules for echo tool
                        "message": ["hello", "world", "test"]
                    },
                    "add": {  # Specific rules for add tool
                        "a": ["range:1-100"],
                        "b": ["range:1-100"]
                    }
                },
                strict=False
            )
            
            # Use the focused client
            result = await focus_client.call_tool("echo", {"message": "hello"})
            print(f"Result: {result.content}")

if __name__ == "__main__":
    asyncio.run(main())

JWT Context Extraction

from mimory_mcp_focus import extract_mcp_context_jwt, extract_mcp_composite_context_jwt

# Extract simple context from JWT
jwt_token = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9..."
jwt_key = "your-secret-key"
jwt_algorithm = "HS256"

context_params, tools_allowed = extract_mcp_context_jwt(
    jwt_token=jwt_token,
    jwt_key=jwt_key,
    jwt_signing_algorithm=jwt_algorithm,
    parameter_field="context",
    tool_field="tools",
    strict=True
)

print(f"Context params: {context_params}")
print(f"Tools allowed: {tools_allowed}")

# Extract composite context from JWT
composite_context = extract_mcp_composite_context_jwt(
    jwt_token=jwt_token,
    jwt_key=jwt_key,
    jwt_signing_algorithm=jwt_algorithm,
    composite_context_field="mcp_focus"
)

print(f"Composite context: {composite_context}")

Refocusing a Client

You can change the focus of an existing client without creating a new one:

from mimory_mcp_focus import refocus_client_simple, refocus_client_composite

# Refocus with simple configuration
refocus_client_simple(
    session=focus_client,
    focus_tools=["echo"],  # Now only allow echo
    focus_params={"message": ["hello"]},  # Only allow "hello" messages
    strict=True
)

# Refocus with composite configuration
refocus_client_composite(
    session=focus_client,
    focus={
        "echo": {"message": ["world", "test"]}
    },
    strict=False
)

API Reference

FocusedClientSession

A focus client that wraps a ClientSession and applies focus restrictions. This is the main class returned by the factory functions.

Methods

• list_tools(cursor: str | None = None): List available tools (filtered by focus rules)
• call_tool(tool_name: str, arguments: Dict[str, Any], **kwargs): Call a tool with parameter validation
• refocus(focus: Dict[str, Any], focus_type: str): Update focus configuration
• All other ClientSession methods are proxied through

focus_client_simple

Factory function that focuses a ClientSession and returns a FocusedClientSession with simple focus configuration.

focus_client_simple(
    session: ClientSession,
    focus_tools: Optional[List[str]] = None,
    focus_params: Optional[Dict[str, Union[str, List[str]]]] = None,
    strict: bool = False
) -> FocusedClientSession

Parameters:

• session: The underlying MCP ClientSession
• focus_tools: List of allowed tool names. Use ["*"] to allow all tools
• focus_params: Dictionary mapping parameter names to allowed values
• strict: If True, all parameters must be defined in focus_params

focus_client_composite

Factory function that focuses a ClientSession and returns a FocusedClientSession with composite focus configuration.

focus_client_composite(
    session: ClientSession,
    focus: Optional[Dict[str, Dict[str, List[str]]]] = None,
    strict: bool = False
) -> FocusedClientSession

Parameters:

• session: The underlying MCP ClientSession
• focus: Dictionary with tool-specific and global focus rules
• strict: If True, all parameters must be defined in focus rules

Focus Dictionary Structure

{
    "tool_name": {  # Tool-specific rules
        "param_name": ["allowed_value"]
    }
}

refocus_client_simple

Refocus an existing FocusedClientSession with new simple focus configuration.

refocus_client_simple(
    session: FocusedClientSession,
    focus_tools: List[str],
    focus_params: Dict[str, Union[str, List[str]]],
    strict: bool
) -> None

refocus_client_composite

Refocus an existing FocusedClientSession with new composite focus configuration.

refocus_client_composite(
    session: FocusedClientSession,
    focus: Dict[str, Dict[str, List[str]]],
    strict: bool
) -> None

JWT Extraction Functions

extract_mcp_context_jwt

Extract simple context parameters and tools from a JWT token.

extract_mcp_context_jwt(
    jwt_token: str,
    jwt_key: str,
    jwt_signing_algorithm: str,
    parameter_field: str = 'context',
    tool_field: str = 'tools',
    strict: bool = False
) -> Tuple[Dict[str, Union[str, List[str]]], List[str]]

Returns:

• focus_params: Dictionary of context parameters
• focus_tools: List of allowed tools

extract_mcp_composite_context_jwt

Extract composite context dictionary from a JWT token.

extract_mcp_composite_context_jwt(
    jwt_token: str,
    jwt_key: str,
    jwt_signing_algorithm: str,
    composite_context_field: str
) -> Dict[str, Dict[str, List[str]]]

Returns:

• focus_composite: The composite context dictionary from the JWT

Parameter Value Types

String Values

"message": ["hello", "world", "test"]

Numeric Ranges

"number": ["range:1-100"]  # Any number between 1 and 100 (inclusive)
"price": ["range:0.01-999.99"]  # Decimal ranges supported

Wildcard

"any_value": ["*"]  # Allow any value

Comma-separated Strings

"tags": "tag1,tag2,tag3"  # Automatically split into ["tag1", "tag2", "tag3"]

Error Handling

The library returns focus-related errors as CallToolResult with isError=True. It raises ValueExceptions and ValidationExceptions depending on internal errors.

result = await focus_client.call_tool("echo", {"message": "forbidden"})
if result.isError:
    print(f"Focus error: {result.content[0].text}")

For JWT extraction functions, the library raises ValueError for validation failures:

from mimory_mcp_focus import extract_mcp_context_jwt

try:
    context_params, tools_allowed = extract_mcp_context_jwt(
        jwt_token="invalid_token",
        jwt_key="secret",
        jwt_signing_algorithm="HS256"
    )
except ValueError as e:
    print(f"JWT validation error: {e}")

Common focus-related error scenarios:

• Tool not in allowed list
• Parameter value not allowed
• Missing required parameter in strict mode

Common exception scenarios:

• Malformed focus_params, focus_tools, or focus fields
• JWT validation failures (expired tokens, invalid signatures, etc.)

Examples

See the examples/ directory for complete working examples:

• basic_usage.py - Basic FocusClient usage
• composite_focus.py - FocusClientComposite usage
• jwt_integration.py - JWT context extraction

Requirements

• Python >= 3.10
• mcp >= 1.14.0
• pyjwt >= 2.10.1

License

MIT License

Author

Travis McQueen - oss@mimory.io

Repository

https://github.com/mimoryinc/mimory-mcp-focus