googleapis/mcp-toolbox · error

toolbox crashed with the following error: %w

Error message

toolbox crashed with the following error: %w

What it means

When the server runs in a goroutine, runtime errors are sent to the srvErr channel. run() selects on srvErr and, if the server returned a non-nil error during serving (request handler panic surfacing, listener failure mid-run), wraps it as 'toolbox crashed with the following error'. The root cause is in the wrapped %w error.

Source

Thrown at cmd/root.go:520

			err = s.Serve(ctx)
			if err != nil {
				srvErr <- err
			}
		}()
	}

	if isCustomConfigured && !opts.Cfg.DisableReload {
		watchDirs, watchedFiles := resolveWatcherInputs(opts.Config, opts.Configs, opts.ConfigFolder)

		// start watching the file(s) or folder for changes to trigger dynamic reloading
		go watchChanges(ctx, watchDirs, watchedFiles, s, opts)
	}

	// wait for either the server to error out or the command's context to be canceled
	select {
	case err := <-srvErr:
		if err != nil {
			errMsg := fmt.Errorf("toolbox crashed with the following error: %w", err)
			opts.Logger.ErrorContext(ctx, errMsg.Error())
			return errMsg
		}
	case <-ctx.Done():
		shutdownContext, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		opts.Logger.WarnContext(shutdownContext, "Shutting down gracefully...")
		err := s.Shutdown(shutdownContext)
		if err == context.DeadlineExceeded {
			return fmt.Errorf("graceful shutdown timed out... forcing exit")
		}
	}

	return nil
}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Inspect the wrapped cause in the logs for the real failure
2. Restart the service and monitor for recurring crashes
3. Check host resource/port/TLS state at crash time
4. Upgrade to the latest toolbox release in case the crash is a known bug

// supervise the toolbox process and react to crash
if err := cmd.Run(); err != nil {
    if strings.Contains(errString, "toolbox crashed with the following error") {
        log.Printf("crash cause: %v; restarting with backoff", err)
        time.Sleep(backoff)
        // retry with bounded attempts
    }
}

When it happens

Trigger: The running server goroutine sends a non-nil error to srvErr while handling traffic or while the listener breaks unexpectedly.

Common situations: Underlying port closed externally, TLS termination failure, or handler-level errors that escalate to the server loop in long-running deployments.

Related errors

• toolbox crashed with the following error: %w
• toolbox failed to initialize: %w
• toolbox failed to start listener: %w
• graceful shutdown timed out... forcing exit
• unable to validate reloaded edits: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/1c3013e54068e4ff. Report an issue: GitHub.