fix: validate MCP tool exists before execution #7632

roomote · 2025-09-03T16:48:28Z

Summary

This PR addresses Issue #7631 by adding validation to prevent Roo from calling MCP tools that don't exist on a server.

Problem

Previously, when the model requested a non-existent tool on an MCP server, the request would be sent to the server anyway, resulting in a raw error response being displayed to the user.

Solution

Added validation that checks if the requested tool exists on the MCP server before attempting to execute it. If the tool doesn't exist:

The request is rejected immediately without contacting the MCP server
A helpful error message is displayed listing all available tools on that server
The model can then retry with a valid tool name

Changes

Added validateToolExists function in useMcpToolTool.ts to check tool availability
Integrated validation into the tool execution flow
Added comprehensive error messages with available tool listings
Added i18n support for the new error messages
Added unit tests covering multiple scenarios (unknown tools, servers with no tools, valid tools)

Testing

✅ All existing tests pass
✅ Added 3 new test cases for tool validation
✅ Manually tested with MCP servers
✅ Type checking passes
✅ Linting passes

Fixes #7631

Important

Adds validation in useMcpToolTool.ts to check MCP tool existence before execution, with error handling and i18n support.

Behavior:
- Adds validateToolExists in useMcpToolTool.ts to check tool existence on MCP server before execution.
- Rejects requests for non-existent tools with error messages listing available tools.
- Handles unknown servers by listing available servers.
Error Handling:
- Displays error messages for unknown tools and servers in responses.ts.
- Adds i18n support for error messages in multiple languages.
Testing:
- Adds unit tests in useMcpToolTool.spec.ts for tool validation scenarios (unknown tools, no tools, valid tools).
- Ensures all existing tests pass.

^{This description was created by}^{for 97945bd. You can customize this summary. It will automatically update as commits are pushed.}

- Add validation to check if requested tool exists on the MCP server - Provide helpful error messages with list of available tools - Prevent sending requests for non-existent tools to MCP servers - Add comprehensive tests for the new validation logic Fixes #7631

roomote

Reviewed my own code. Found it disturbingly functional. Clearly a glitch in the matrix.

roomote · 2025-09-03T16:54:23Z

src/core/tools/useMcpToolTool.ts

+
+		if (!server) {
+			// Server not found - this will be caught later in the flow
+			return { isValid: true }


Is this intentional? When the server is not found, returning { isValid: true } allows execution to continue. Should we fail validation here instead to prevent unnecessary API calls?

roomote · 2025-09-03T16:54:23Z

src/core/tools/useMcpToolTool.ts

+	} 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
+		console.error("Error validating MCP tool existence:", error)


Consider surfacing validation errors to users for better debugging visibility. The error is only logged to console which might make troubleshooting harder.

roomote · 2025-09-03T16:54:23Z

src/core/tools/__tests__/useMcpToolTool.spec.ts

 			expect(mockHandleError).toHaveBeenCalledWith("executing MCP tool", error)
 		})
+
+		it("should reject unknown tool names", async () => {


Consider adding a test case for when the MCP hub itself is unavailable to ensure the fallback behavior works correctly.

…d tests

daniel-lxs

LGTM

mrubens · 2025-09-04T16:32:34Z

src/core/tools/useMcpToolTool.ts

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


Does this take into account tools that the user has disabled?

take into account tools that the user has disabled

@mrubens

After the bug fix release, I see that disabled tools are being ignored, and the prompt mentions all tools, including the disabled ones.

I have additionally checked the system prompt, and everything is correct there - disabled tools are not included in the description.

- Check enabledForPrompt property in validateToolExists function - Reject disabled tools with appropriate error message - Show only enabled tools in error message when tool is disabled Addresses PR feedback about checking for disabled tools

ellipsis-dev · 2025-09-04T20:48:04Z

src/core/tools/useMcpToolTool.ts

+			cline.recordToolError("use_mcp_tool")
+			await cline.say(
+				"error",
+				`Tool '${toolName}' on server '${serverName}' is disabled. Available enabled tools: ${enabledToolNames.length > 0 ? enabledToolNames.join(", ") : "No enabled tools available"}`,


Consider using the i18n translation function (t()) for the disabled tool error message instead of an inline string. For consistency with the tool-not-found error (which uses t('mcp:errors.toolNotFound')), refactor this error message (and the "No enabled tools available" text) to use a translation key (e.g., t('mcp:errors.toolDisabled', { toolName, serverName, enabledTools: enabledToolNames.join(", ") })) so that the message supports multiple languages.

Suggested change

`Tool '${toolName}' on server '${serverName}' is disabled. Available enabled tools: ${enabledToolNames.length > 0 ? enabledToolNames.join(", ") : "No enabled tools available"}`,

t('mcp:errors.toolDisabled', { toolName, serverName, enabledTools: enabledToolNames.length > 0 ? enabledToolNames.join(", ") : "No enabled tools available" }),

^{This comment was generated because it violated a code review rule: irule_C0ez7Rji6ANcGkkX.}

- Replace hardcoded error message with t() translation function - Add toolDisabled translation key to all 17 locale files - Maintains proper placeholder variables for code integration

roomote bot requested review from cte, jr and mrubens as code owners September 3, 2025 16:48

github-project-automation bot added this to Roo Code Roadmap and Roo Code Roadmap Sep 3, 2025

github-project-automation bot moved this to Triage in Roo Code Roadmap Sep 3, 2025

github-project-automation bot moved this to New in Roo Code Roadmap Sep 3, 2025

dosubot bot added size:L This PR changes 100-499 lines, ignoring generated files. bug Something isn't working labels Sep 3, 2025

roomote bot commented Sep 3, 2025

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roomote bot mentioned this pull request Sep 3, 2025

Roo may call mcp tool that is known not to exist. #7631

Closed

hannesrudolph added the Issue/PR - Triage New issue. Needs quick review to confirm validity and assign labels. label Sep 3, 2025

daniel-lxs moved this from Triage to PR [Needs Prelim Review] in Roo Code Roadmap Sep 4, 2025

hannesrudolph added PR - Needs Preliminary Review and removed Issue/PR - Triage New issue. Needs quick review to confirm validity and assign labels. labels Sep 4, 2025

fix(mcp): fail fast on unknown server; add i18n keys/translations; ad…

326268a

…d tests

daniel-lxs moved this from PR [Needs Prelim Review] to PR [Needs Review] in Roo Code Roadmap Sep 4, 2025

daniel-lxs approved these changes Sep 4, 2025

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dosubot bot added the lgtm This PR has been approved by a maintainer label Sep 4, 2025

hannesrudolph added PR - Needs Review and removed PR - Needs Preliminary Review labels Sep 4, 2025

mrubens reviewed Sep 4, 2025

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ellipsis-dev bot reviewed Sep 4, 2025

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fix: use translation for disabled tool error message

97945bd

- Replace hardcoded error message with t() translation function - Add toolDisabled translation key to all 17 locale files - Maintains proper placeholder variables for code integration

mrubens approved these changes Sep 4, 2025

View reviewed changes

mrubens merged commit 7935c94 into main Sep 4, 2025
9 checks passed

github-project-automation bot moved this from New to Done in Roo Code Roadmap Sep 4, 2025

github-project-automation bot moved this from PR [Needs Review] to Done in Roo Code Roadmap Sep 4, 2025

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fix: validate MCP tool exists before execution #7632

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	`Tool '${toolName}' on server '${serverName}' is disabled. Available enabled tools: ${enabledToolNames.length > 0 ? enabledToolNames.join(", ") : "No enabled tools available"}`,
	t('mcp:errors.toolDisabled', { toolName, serverName, enabledTools: enabledToolNames.length > 0 ? enabledToolNames.join(", ") : "No enabled tools available" }),

fix: validate MCP tool exists before execution #7632

fix: validate MCP tool exists before execution #7632

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roomote bot commented Sep 3, 2025 •

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