CoplayDev/unity-mcp · error · InvalidOperationException

Failed to register with Claude Code: {stderr} {stdout}

Error message

Failed to register with Claude Code:
{stderr}
{stdout}

What it means

RegisterWithCapturedValues() runs `claude mcp add --scope local ...` via ExecPath.TryRun with a 15-second timeout. If the process exits non-zero (TryRun returns false), it throws InvalidOperationException embedding both stderr and stdout. The actual failure reason is in the stderr text — common causes include invalid arguments, authentication errors, scope conflicts, or the binary being present but broken.

Source

Thrown at MCPForUnity/Editor/Clients/McpClientConfiguratorBase.cs:920

                else
                {
                    args = $"mcp add --scope local --transport http UnityMCP {httpUrl}";
                }
            }
            else
            {
                // Use --scope local to register in the project-local config, avoiding conflicts with user-level config (#664)
                args = $"mcp add --scope local --transport stdio UnityMCP -- \"{uvxPath}\" {uvxDevFlags}{fromArgs} {packageName}";
            }

            // Remove any existing registrations from ALL scopes to prevent stale config conflicts (#664)
            McpLog.Info("Removing any existing UnityMCP registrations from all scopes before adding...");
            RemoveFromAllScopes(claudePath, projectDir, pathPrepend);

            // Now add the registration
            if (!ExecPath.TryRun(claudePath, args, projectDir, out var stdout, out var stderr, 15000, pathPrepend))
            {
                throw new InvalidOperationException($"Failed to register with Claude Code:\n{stderr}\n{stdout}");
            }

            McpLog.Info($"Successfully registered with Claude Code using {(useHttpTransport ? "HTTP" : "stdio")} transport.");
            client.SetStatus(McpStatus.Configured);
            client.configuredTransport = serverTransport;
        }

        /// <summary>
        /// Thread-safe unregistration using pre-captured values.
        /// </summary>
        private void UnregisterWithCapturedValues(string projectDir, string claudePath, string pathPrepend)
        {
            if (string.IsNullOrEmpty(claudePath))
            {
                throw new InvalidOperationException("Claude CLI not found. Please install Claude Code first.");
            }

            // Remove from ALL scopes to ensure complete cleanup (#664)

View on GitHub (pinned to c21bf496bc)

Solutions

1. Read the stderr in the exception message — it contains the exact CLI error.
2. Update Claude Code to the latest version: `npm update -g @anthropic-ai/claude-code`.
3. Run the exact `claude mcp add` command from GetManualSnippet() manually in a terminal to see the full error output.
4. If a stale registration conflicts, run `claude mcp remove UnityMCP` in all scopes before retrying.
5. For timeout issues, check if Claude CLI is prompting for input interactively (it cannot in a subprocess).

try { configurator.Configure(); }
catch (InvalidOperationException ex)
{ Debug.LogError($"Claude registration failed:\n{ex.Message}"); ShowManualSnippet(); }

When it happens

Trigger: The `claude mcp add` subprocess fails: wrong CLI version (missing --scope or --transport flags), malformed URL, authentication required, the binary exists but errors at runtime, or the 15-second timeout is exceeded.

Common situations: Claude Code CLI version mismatch (older version without --scope local support). The HTTP URL is malformed or unreachable. A stale registration in a different scope blocks the add. The process exceeds the 15-second timeout on a slow machine.

Related errors

• Claude CLI not found. Please install Claude Code first.
• Cherry Studio uses UI-based configuration. Please use the Ma
• OpenClaw config contains non-JSON content and cannot be safe
• uvx not found. Install uv/uvx or set the override in Advance
• uvx not found. Install uv/uvx or set the override in Advance

AI-assisted analysis of CoplayDev/unity-mcp@c21bf496bc (2026-08-13). Data as JSON: /api/errors/1da71e5adcfb7776. Report an issue: GitHub.