URL Parameters Not Decoded in Dynamic Resources

[codeonym]

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

Dynamic URL resource parameters in MCP protocol are not automatically URL-decoded, causing encoded characters (like %20 for spaces and %C3%A9 for accented characters) to be passed as-is to resource handlers instead of their decoded equivalents.

Here is a simple log for the bug:

• before

2025-06-17 14:43:44,385 [INFO] kn-graph: Found 0 products matching 'stick%20correcteur%20teint%C3%A9%20anti-imperfections%20rechargeable%20au%20zinc' - (logger.py:226)

• after explicit decode

2025-06-17 14:55:10,173 [INFO] kn-graph: Found 10 products matching 'stick correcteur teinté anti-imperfections rechargeable au zinc' - (logger.py:226)

Example Code

@mcp.resource("products://search/{product_identifier}")
    def find_similar_products(product_identifier: str):
        """
        Find similar products based on a given product identifier.
        :param product_identifier: The identifier of the product (product name or code).
        :return: Similar products or an error message if none are found.
        """
        print(product_identifier)
        """
         -- walkaround: explicit decoding
        from urllib.parse import unquote
        print(unquote(product_identifier))
        """

Python & MCP Python SDK

# uv pip list | grep "mcp"
mcp                          1.9.2
# python --version
Python 3.13.4

[felixweinberger]

Working on this as part of Python SDK v2 hackathon.

[codeonym]

hey @felixweinberger , thanks for addressing that one out