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- 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
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