fix: don't duplicate built-in tools in system prompt when MCP tools present#11068
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shanevcantwell wants to merge 1 commit intocontinuedev:mainfrom
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fix: don't duplicate built-in tools in system prompt when MCP tools present#11068shanevcantwell wants to merge 1 commit intocontinuedev:mainfrom
shanevcantwell wants to merge 1 commit intocontinuedev:mainfrom
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…resent Fix continuedev#11064 When MCP/dynamic tools are registered alongside built-in tools, generateToolsSystemMessage() listed ALL tools through toolToSystemToolDefinition instead of only the dynamic ones. Built-in tools appeared twice — once via their systemMessageDescription (predefined section) and again via the dynamic section. Found while auditing the system message tools framework for local model compatibility. Duplicate definitions waste context tokens and send contradictory format information that frontier models silently handle but local models struggle with. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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This was referenced Mar 5, 2026
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Summary
generateToolsSystemMessage()duplicates all built-in tools in the system prompt when any MCP/dynamic tool is registered alongside themThe bug
buildToolsSystemMessage.tsline 43 iteratestools(all tools) instead ofwithDynamicMessage(only tools withoutsystemMessageDescription). When thewithDynamicMessage.length > 0branch fires, every built-in tool gets listed twice:createSystemMessageExampleCall()(usingsystemMessageDescription.prefix+ example args)toolToSystemToolDefinition()(usingtool_definitioncodeblock format)The
withDynamicMessagevariable is computed on lines 18-20 for exactly this purpose — it just wasn't used.Context
Found while auditing the system message tools framework for local model compatibility. Duplicate definitions waste context tokens and send contradictory format information (predefined uses example calls, dynamic uses
tool_definitionblocks). Frontier models silently handle the redundancy; local models with smaller context windows are disproportionately affected.Changes
core/tools/systemMessageTools/buildToolsSystemMessage.tstools→withDynamicMessageon line 43core/tools/systemMessageTools/toolCodeblocks/buildSystemMessage.vitest.tsTest plan
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Summary by cubic
Fix duplicated built-in tool definitions in the system prompt when MCP/dynamic tools are present, reducing token waste and conflicting instructions. Fixes #11064 by listing only dynamic tools in the additional definitions section and adds a test to ensure no duplicates.
Written for commit 9702f31. Summary will update on new commits.