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fix: handle MCP tool names with hyphens in native tool calling #10643

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fix: handle MCP tool names with hyphens in native tool calling #10643

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11 changes: 4 additions & 7 deletions src/core/assistant-message/NativeToolCallParser.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ import type {
ApiStreamToolCallDeltaChunk,
ApiStreamToolCallEndChunk,
} from "../../api/transform/stream"
import { MCP_TOOL_PREFIX, MCP_TOOL_SEPARATOR, parseMcpToolName } from "../../utils/mcp-name"
import { isMcpTool, parseMcpToolName } from "../../utils/mcp-name"

/**
* Helper type to extract properly typed native arguments for a given tool.
Expand Down Expand Up @@ -242,8 +242,7 @@ export class NativeToolCallParser {
toolCall.argumentsAccumulator += chunk

// For dynamic MCP tools, we don't return partial updates - wait for final
const mcpPrefix = MCP_TOOL_PREFIX + MCP_TOOL_SEPARATOR
if (toolCall.name.startsWith(mcpPrefix)) {
if (isMcpTool(toolCall.name)) {
return null
}

Expand Down Expand Up @@ -574,10 +573,8 @@ export class NativeToolCallParser {
name: TName
arguments: string
}): ToolUse<TName> | McpToolUse | null {
// Check if this is a dynamic MCP tool (mcp--serverName--toolName)
const mcpPrefix = MCP_TOOL_PREFIX + MCP_TOOL_SEPARATOR

if (typeof toolCall.name === "string" && toolCall.name.startsWith(mcpPrefix)) {
// Check if this is a dynamic MCP tool (mcp--serverName--toolName or mcp__serverName__toolName)
if (typeof toolCall.name === "string" && isMcpTool(toolCall.name)) {
return this.parseDynamicMcpTool(toolCall)
}

Expand Down
75 changes: 51 additions & 24 deletions src/core/tools/UseMcpToolTool.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import { Task } from "../task/Task"
import { formatResponse } from "../prompts/responses"
import { t } from "../../i18n"
import type { ToolUse } from "../../shared/tools"
import { findMatchingServerName, findMatchingToolName } from "../../utils/mcp-name"

import { BaseTool, ToolCallbacks } from "./BaseTool"

Expand Down Expand Up @@ -53,14 +54,18 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
return
}

// Use resolved names (handles model-mangled names like underscores instead of hyphens)
const resolvedServerName = toolValidation.resolvedServerName ?? serverName
const resolvedToolName = toolValidation.resolvedToolName ?? toolName

// Reset mistake count on successful validation
task.consecutiveMistakeCount = 0

// Get user approval
// Get user approval (show resolved names to user)
const completeMessage = JSON.stringify({
type: "use_mcp_tool",
serverName,
toolName,
serverName: resolvedServerName,
toolName: resolvedToolName,
arguments: params.arguments ? JSON.stringify(params.arguments) : undefined,
} satisfies ClineAskUseMcpServer)

Expand All @@ -71,11 +76,11 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
return
}

// Execute the tool and process results
// Execute the tool with resolved names
await this.executeToolAndProcessResult(
task,
serverName,
toolName,
resolvedServerName,
resolvedToolName,
parsedArguments,
executionId,
pushToolResult,
Expand Down Expand Up @@ -156,7 +161,12 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
serverName: string,
toolName: string,
pushToolResult: (content: string) => void,
): Promise<{ isValid: boolean; availableTools?: string[] }> {
): Promise<{
isValid: boolean
availableTools?: string[]
resolvedServerName?: string
resolvedToolName?: string
}> {
try {
// Get the MCP hub to access server information
const provider = task.providerRef.deref()
Expand All @@ -168,12 +178,16 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
}

// Get all servers to find the specific one
// Use fuzzy matching to handle model-mangled names (hyphens converted to underscores)
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@pdecat pdecat Jan 12, 2026

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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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@pdecat pdecat Jan 12, 2026

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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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@daniel-lxs daniel-lxs Jan 12, 2026

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You can submit it if you'd like

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@pdecat pdecat Jan 12, 2026

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Thanks, submitted #10644

const servers = mcpHub.getAllServers()
const server = servers.find((s) => s.name === serverName)
const availableServersArray = servers.map((s) => s.name)

// Try fuzzy matching for server name
const matchedServerName = findMatchingServerName(serverName, availableServersArray)
const server = matchedServerName ? servers.find((s) => s.name === matchedServerName) : null

if (!server) {
if (!server || !matchedServerName) {
// Fail fast when server is unknown
const availableServersArray = servers.map((s) => s.name)
const availableServers =
availableServersArray.length > 0 ? availableServersArray.join(", ") : "No servers available"

Expand All @@ -186,6 +200,9 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
return { isValid: false, availableTools: [] }
}

// At this point, matchedServerName is guaranteed to be non-null
const resolvedServerName = matchedServerName

// Check if the server has tools defined
if (!server.tools || server.tools.length === 0) {
// No tools available on this server
Expand All @@ -195,39 +212,42 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
"error",
t("mcp:errors.toolNotFound", {
toolName,
serverName,
serverName: resolvedServerName,
availableTools: "No tools available",
}),
)
task.didToolFailInCurrentTurn = true

pushToolResult(formatResponse.unknownMcpToolError(serverName, toolName, []))
pushToolResult(formatResponse.unknownMcpToolError(resolvedServerName, toolName, []))
return { isValid: false, availableTools: [] }
}

// Check if the requested tool exists
const tool = server.tools.find((tool) => tool.name === toolName)
// Check if the requested tool exists using fuzzy matching
const availableToolNames = server.tools.map((tool) => tool.name)
const matchedToolName = findMatchingToolName(toolName, availableToolNames)
const tool = matchedToolName ? server.tools.find((t) => t.name === matchedToolName) : null

if (!tool) {
if (!tool || !matchedToolName) {
// Tool not found - provide list of available tools
const availableToolNames = server.tools.map((tool) => tool.name)

task.consecutiveMistakeCount++
task.recordToolError("use_mcp_tool")
await task.say(
"error",
t("mcp:errors.toolNotFound", {
toolName,
serverName,
serverName: resolvedServerName,
availableTools: availableToolNames.join(", "),
}),
)
task.didToolFailInCurrentTurn = true

pushToolResult(formatResponse.unknownMcpToolError(serverName, toolName, availableToolNames))
pushToolResult(formatResponse.unknownMcpToolError(resolvedServerName, toolName, availableToolNames))
return { isValid: false, availableTools: availableToolNames }
}

// At this point, matchedToolName is guaranteed to be non-null
const resolvedToolName = matchedToolName

// Check if the tool is disabled (enabledForPrompt is false)
if (tool.enabledForPrompt === false) {
// Tool is disabled - only show enabled tools
Expand All @@ -239,20 +259,27 @@ export class UseMcpToolTool extends BaseTool<"use_mcp_tool"> {
await task.say(
"error",
t("mcp:errors.toolDisabled", {
toolName,
serverName,
toolName: resolvedToolName,
serverName: resolvedServerName,
availableTools:
enabledToolNames.length > 0 ? enabledToolNames.join(", ") : "No enabled tools available",
}),
)
task.didToolFailInCurrentTurn = true

pushToolResult(formatResponse.unknownMcpToolError(serverName, toolName, enabledToolNames))
pushToolResult(
formatResponse.unknownMcpToolError(resolvedServerName, resolvedToolName, enabledToolNames),
)
return { isValid: false, availableTools: enabledToolNames }
}

// Tool exists and is enabled
return { isValid: true, availableTools: server.tools.map((tool) => tool.name) }
// Tool exists and is enabled - return resolved names for execution
return {
isValid: true,
availableTools: server.tools.map((tool) => tool.name),
resolvedServerName,
resolvedToolName,
}
} catch (error) {
// If there's an error during validation, log it but don't block the tool execution
// The actual tool call might still fail with a proper error
Expand Down
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