{"record":{"id":"c8cbc0865b1eff45","repo":"langflow-ai/langflow","slug":"failed-to-start-mcp-composer-see-logs-for-details","errorCode":null,"errorMessage":"Failed to start MCP Composer. See logs for details.","messagePattern":"Failed to start MCP Composer\\. See logs for details\\.","errorType":"http","errorClass":"HTTPException","httpStatus":500,"severity":"error","filePath":"src/backend/base/langflow/api/v1/mcp_projects.py","lineNumber":894,"sourceCode":"            raise HTTPException(status_code=400, detail=\"Invalid transport. Use 'sse' or 'streamablehttp'.\")\n\n        if use_mcp_composer:\n            try:\n                auth_config = await _get_mcp_composer_auth_config(project)\n                await get_or_start_mcp_composer(auth_config, project.name, project_id)\n                composer_streamable_http_url = await get_composer_streamable_http_url(project)\n                sse_url = await get_composer_sse_url(project)\n                connection_urls = [composer_streamable_http_url, sse_url]\n            except MCPComposerError as e:\n                await logger.aerror(\n                    f\"Failed to start MCP Composer for project '{project.name}' ({project_id}): {e.message}\"\n                )\n                raise HTTPException(status_code=500, detail=e.message) from e\n            except Exception as e:\n                error_msg = f\"Failed to start MCP Composer for project '{project.name}' ({project_id}): {e!s}\"\n                await logger.aerror(error_msg)\n                error_detail = \"Failed to start MCP Composer. See logs for details.\"\n                raise HTTPException(status_code=500, detail=error_detail) from e\n\n            # For OAuth/MCP Composer, use the special format\n            settings = get_settings_service().settings\n            command = \"uvx\"\n            args = [\n                *mcp_sdk_constraint_args(),\n                f\"mcp-composer{settings.mcp_composer_version}\",\n                \"--mode\",\n                \"http\",\n                \"--endpoint\",\n                composer_streamable_http_url,\n                \"--sse-url\",\n                sse_url,\n                \"--client_auth_type\",\n                \"oauth\",\n                \"--disable-composer-tools\",\n            ]\n        else:","sourceCodeStart":876,"sourceCodeEnd":912,"githubUrl":"https://github.com/langflow-ai/langflow/blob/976ec789d2886a86de109c044d089d68e96c9a35/src/backend/base/langflow/api/v1/mcp_projects.py#L876-L912","documentation":"Error \"Failed to start MCP Composer. See logs for details.\" thrown in langflow-ai/langflow.","triggerScenarios":"Occurs when the MCP Composer process fails to start; details are only available in server logs.","commonSituations":"See trigger scenarios.","solutions":["Check the Langflow logs for the MCP Composer startup failure; verify the required binaries are installed."],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"976ec789d2886a86de109c044d089d68e96c9a35","analyzedAt":"2026-08-14T18:23:12.227Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}