fix: handle MCP tool names with hyphens in native tool calling #10643
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When models like Claude Opus 4.5 use native tool calling, they convert hyphens to underscores in function names. This causes MCP tool names like mcp--atlassian-jira--search to be returned as mcp__atlassian_jira__search. Changes: - Add MCP_TOOL_SEPARATOR_MANGLED constant to recognize __ separator - Update isMcpTool() to recognize both mcp-- and mcp__ prefixes - Update parseMcpToolName() to handle both separator formats - Add generatePossibleOriginalNames() for underscore-to-hyphen combinations - Add findMatchingServerName() and findMatchingToolName() for fuzzy matching - Integrate fuzzy matching in UseMcpToolTool.validateToolExists() Fixes: #10642
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Review complete. No issues found. The implementation correctly handles MCP tool names with hyphens when models convert them to underscores in native tool calling. The fix includes:
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hannesrudolph
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pdecat
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Jan 12, 2026
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| // Get all servers to find the specific one | ||
| // Use fuzzy matching to handle model-mangled names (hyphens converted to underscores) |
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I didn't like the fuzzy option Claude proposed me at first, so I proposed to encode the hyphens, see pdecat#1
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FWIW, I did not submit the PR as I was waiting for my issue to be accepted.
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Closing in favor of #10644 |
daniel-lxs
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feature/roo-496-fix-mcp-tool-names-with-hyphens-failing-in-native-tool
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Problem
When models like Claude Opus 4.5 use native tool calling, they convert hyphens to underscores in function names. This causes MCP tool names like
mcp--atlassian-jira--searchto be returned asmcp__atlassian_jira__search, which the parser rejected as invalid.Solution
Implemented separator normalization AND fuzzy matching for server/tool name recovery:
1. Separator Normalization
isMcpTool()recognizes bothmcp--andmcp__prefixesparseMcpToolName()handles both separator formats and returnswasMangledflag2. Server/Tool Name Recovery (via fuzzy matching)
generatePossibleOriginalNames()generates all underscore-to-hyphen combinations (2^n, limited to 8 underscores)findMatchingServerName()fuzzy matchesatlassian_jira→atlassian-jirafindMatchingToolName()same for tool namesUseMcpToolTool.validateToolExists()integrates fuzzy matchingFiles Modified
src/utils/mcp-name.ts- Separator constants, parsing, fuzzy matching functionssrc/core/assistant-message/NativeToolCallParser.ts- UseisMcpTool()for detectionsrc/core/tools/UseMcpToolTool.ts- Integrate fuzzy matching for name resolutionsrc/utils/__tests__/mcp-name.spec.ts- 56 tests including end-to-end issue scenariosTest Results
All tests pass: 5215 passed, 49 skipped
Fixes #10642
Linear: ROO-496
Important
Fixes MCP tool name mangling by implementing separator normalization and fuzzy matching for name recovery.
isMcpTool()inmcp-name.tsnow recognizes bothmcp--andmcp__prefixes.parseMcpToolName()handles both separator formats and returnswasMangledflag.generatePossibleOriginalNames()creates combinations of underscore-to-hyphen replacements.findMatchingServerName()andfindMatchingToolName()perform fuzzy matching.UseMcpToolTool.validateToolExists()integrates fuzzy matching.mcp-name.ts: Added separator constants, parsing, and fuzzy matching functions.NativeToolCallParser.ts: UsesisMcpTool()for detection.UseMcpToolTool.ts: Integrates fuzzy matching for name resolution.mcp-name.spec.ts: 56 tests including end-to-end issue scenarios.This description was created by
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