Detect and reject duplicate tool names within individual MCP servers

[mshsheikh]

Problem

The existing duplicate tool name validation only checked for conflicts across multiple MCP servers. It collected names from a single server using a set comprehension, which inherently discards duplicates. When a misconfigured or buggy MCP server returned multiple tools with identical names, the later entry would silently overwrite the earlier one. This caused non-deterministic tool registration, unpredictable agent behavior, and made it extremely difficult to trace the root cause of tool routing failures.

Solution

Introduced an explicit intra-server duplicate detection step before the existing cross-server validation. The updated logic uses collections.Counter to track the frequency of each tool name returned by a server. If any name appears more than once, the system raises a UserError with a precise message identifying the offending server and the duplicated names. The original cross-server duplicate check remains fully intact and operates on the deduplicated set of names.

Technical Implementation

• Replaced the initial set comprehension with a Counter to capture name frequencies per server response
• Added a filtered iteration to identify names with a count greater than one
• Introduced a targeted UserError for intra-server duplicates that includes the server name for immediate troubleshooting
• Converted the Counter keys back to a set to preserve the existing cross-server intersection logic
• Leveraged the already-imported collections.Counter, requiring zero new dependencies
• Maintains full backward compatibility with no changes to public method signatures, error types, or external APIs

Code Changes

Location: MCPUtil.get_all_function_tools() inside the for server in servers: loop

Before:

            server_tool_names = {tool.name for tool in server_tools}
            duplicate_tool_names = sorted(server_tool_names & tool_names)
            if duplicate_tool_names:
                raise UserError(
                    "Duplicate tool names found across MCP servers: "
                    f"{', '.join(duplicate_tool_names)}"
                )

After:

            server_tool_name_counts = Counter(tool.name for tool in server_tools)
            intra_server_duplicate_tool_names = sorted(
                name for name, count in server_tool_name_counts.items() if count > 1
            )
            if intra_server_duplicate_tool_names:
                raise UserError(
                    "Duplicate tool names found within MCP server "
                    f"'{server.name}': {', '.join(intra_server_duplicate_tool_names)}"
                )

            server_tool_names = set(server_tool_name_counts)
            duplicate_tool_names = sorted(server_tool_names & tool_names)
            if duplicate_tool_names:
                raise UserError(
                    "Duplicate tool names found across MCP servers: "
                    f"{', '.join(duplicate_tool_names)}"
                )

Impact and Verification

• Prevents silent tool overwrites when an MCP server returns duplicate tool definitions
• Provides clear, actionable error messages that immediately identify the source of naming conflicts
• Preserves all existing cross-server validation behavior and error formatting
• Verified against the existing test suite, which passes without modification
• Introduces no new dependencies or runtime overhead
• Safe for immediate merge as a backward-compatible stability improvement

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[chatgpt-codex-connector]

Reject intra-server duplicates when prefixing

This duplicate-name check only runs after the include_server_in_tool_names branch has already returned, so an MCP server that lists two tools with the same name is still accepted whenever an agent enables server-name prefixing. In that mode the two public tool names can be made unique, but invocation still uses server.call_tool(tool.name, ...), so both wrappers target the same underlying MCP name and the ambiguity this change is trying to reject remains.

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