Fix allowed_tools filtering to correctly handle empty list - #2
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The allowed_tools parameter in MCPTool.functions and MCP server config helpers used a falsy check (if not allowed_tools / if allowed_tools) which treats an empty list identically to None. This meant passing allowed_tools=[] would bypass filtering and return all tools, rather than returning no tools as expected. Changed to explicit None checks so that: - allowed_tools=None -> no filtering (return all tools) - allowed_tools=[] -> explicit empty allowlist (return no tools) - allowed_tools=[...] -> filter to listed names only Also normalized serialization to use list() for consistency with arbitrary Collection inputs. Co-authored-by: Azure SRE Agent <noreply@microsoft.com>
chetantoshniwal
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Summary
Fixes incorrect behavior where passing
allowed_tools=[]to MCP tool constructors or chat client helpers would expose all tools instead of no tools.Problem
The
MCPTool.functionsproperty and MCP server config helper methods used Python falsy checks (if not self.allowed_tools/if allowed_tools) to determine whether filtering should be applied. Since an empty list[]is falsy in Python, it was treated identically toNone, causing the filter to be skipped entirely.This meant:
allowed_tools=None→ all tools (correct, documented behavior)allowed_tools=["tool_a"]→ only tool_a (correct)allowed_tools=[]→ all tools exposed (incorrect — should return no tools)Fix
Changed to explicit
Nonechecks across 4 files:python/packages/core/agent_framework/_mcp.py— core filtering logicpython/packages/anthropic/agent_framework_anthropic/_chat_client.py— MCP config serializationpython/packages/foundry/agent_framework_foundry/_chat_client.py— MCP config serializationpython/packages/openai/agent_framework_openai/_chat_client.py— MCP config serializationNow:
allowed_tools=None→ no filtering (return all tools)allowed_tools=[]→ explicit empty allowlist (return no tools)allowed_tools=[...]→ filter to listed names onlyAlso normalized serialization to use
list()cast for consistency with arbitraryCollectioninputs.