# Second Opinion MCP

Get second opinions from multiple AI models while using Claude. Break the single-model echo chamber by consulting DeepSeek Reasoner, Kimi K2.5 (Moonshot), OpenAI (ChatGPT), and 300+ OpenRouter models.

## What It Does

When working with Claude Code or Claude Desktop, this MCP server lets you:

- Get alternative perspectives on code, architecture, and decisions
- Run systematic code reviews with severity-classified issues
- Stage multi-model debates where AI models argue opposing positions
- Challenge proposals with anti-sycophancy mode (finds weaknesses, not validation)
- Review architectural plans before coding begins
- Review implementations against their original plans

## Quickstart

### 1. Install

#### Windows

```powershell
# Install Python 3.10+ from python.org if not installed
# Then install pipx
pip install pipx
pipx ensurepath

# Restart your terminal, then install
pipx install second-opinion-mcp
```

#### macOS

```bash
# Install Python 3.10+ via Homebrew if not installed
brew install python@3.12

# Install pipx
pip3 install pipx
pipx ensurepath

# Restart your terminal, then install
pipx install second-opinion-mcp
```

#### Linux (Ubuntu/Debian)

```bash
# Install Python and pipx
sudo apt update
sudo apt install python3 python3-pip python3-venv
pip3 install pipx
pipx ensurepath

# Restart your terminal, then install
pipx install second-opinion-mcp
```

#### Linux (Fedora/RHEL)

```bash
sudo dnf install python3 python3-pip
pip3 install pipx
pipx ensurepath

# Restart your terminal, then install
pipx install second-opinion-mcp
```

### 2. Setup

Run the interactive setup wizard:

```bash
second-opinion-mcp setup
```

The wizard will guide you through selecting providers and entering API keys. Keys are stored securely in your system's credential manager.

The wizard automatically verifies your setup when it finishes. To re-check later:

```bash
second-opinion-mcp verify
```

After setup completes, see Client Integration below for instructions specific to your MCP client.

## Client Integration

After running the setup wizard, register the MCP server with your client.

### Claude Code CLI

Register the server:

```bash
claude mcp add -s user second-opinion -- second-opinion-mcp
```

The server auto-detects which providers have credentials configured (v0.8.0+). To restrict to specific providers, use the env var:

```bash
claude mcp add -s user second-opinion -e SECOND_OPINION_PROVIDERS="deepseek,moonshot" -- second-opinion-mcp
```

Restart Claude Code after registering.

Verify the server is registered:

```bash
claude mcp list | grep second-opinion
```

### Claude Desktop App

Add to your `claude_desktop_config.json`:

**Windows:** `%APPDATA%\Claude\claude_desktop_config.json`

**macOS:** `~/Library/Application Support/Claude/claude_desktop_config.json`

```json
{
  "mcpServers": {
    "second-opinion": {
      "command": "second-opinion-mcp"
    }
  }
}
```

The server auto-detects providers from credentials (v0.8.0+). To restrict to specific providers, add an `env` block with `"SECOND_OPINION_PROVIDERS": "deepseek,moonshot"`.

Restart Claude Desktop after saving. To verify, start a new conversation and check that the second-opinion tools appear in the available tools list.

### OpenClaw

OpenClaw uses mcporter for MCP server integration.

**Step 1: Run the setup wizard**

```bash
second-opinion-mcp setup
```

This stores your API keys in `~/.second-opinion-config`:

```json
{
  "credentials": {
    "deepseek": "sk-...",
    "moonshot": "sk-..."
  }
}
```

**Step 2: Install mcporter**

```bash
npm install -g mcporter
```

**Step 3: Add to mcporter config**

Create or edit `~/.mcporter/mcporter.json`:

```json
{
  "mcpServers": {
    "second-opinion": {
      "command": "second-opinion-mcp",
      "env": {
        "SECOND_OPINION_PROVIDERS": "deepseek,moonshot",
        "SECOND_OPINION_ALLOWED_ROOTS": "/opt/openclaw"
      }
    }
  }
}
```

Note: API keys are NOT in mcporter config. They stay in `~/.second-opinion-config`, separate from server registration.

**Step 4: Verify**

```bash
mcporter list
mcporter tools second-opinion
```

OpenClaw automatically discovers servers configured in mcporter.

### Other MCP Clients

For other MCP-compatible clients, the server requires:

- Command: `second-opinion-mcp`
- Optional: `SECOND_OPINION_PROVIDERS=deepseek,moonshot` to restrict providers (auto-detected from credentials by default)

Refer to your client's documentation for how to add stdio-based MCP servers.

## Supported Models

### DeepSeek V3.2 (Recommended)

Chain-of-thought reasoning model. Best for code reviews and complex analysis.

- Get your API key at https://platform.deepseek.com
- Pricing: ~$0.28/$0.42 per million tokens (input/output)

### Kimi K2.5 (Moonshot)

Chinese AI model with thinking mode. Good for alternative perspectives and debates.

- Get your API key at https://platform.moonshot.ai
- Supports 256K context window

### OpenAI (ChatGPT)

GPT-5.3-codex (OAuth) / GPT-5.2-thinking (API key) with 400K context and 128K output. Good for architectural reviews and implementation analysis.

The recommended way to authenticate is via the built-in OAuth login, which provides free access for ChatGPT Plus subscribers. Run the setup wizard and choose "Login with ChatGPT Plus (OAuth)":

```bash
second-opinion-mcp setup
# Select OpenAI, choose "Login with ChatGPT Plus (OAuth)"
# Browser opens for sign-in, tokens stored automatically
```

On headless systems (SSH, Docker), the wizard uses a device code flow instead: it displays a URL and code to enter on any device with a browser.

Three authentication methods are supported (checked in this order):

1. Built-in OAuth token from setup wizard (free for ChatGPT Plus, stored in `~/.second-opinion-config`)
2. Codex CLI OAuth token from `~/.codex/auth.json` (fallback if Codex CLI is installed)
3. Standard API key from https://platform.openai.com/api-keys (pay-as-you-go)

Tokens are automatically refreshed when expired.

### OpenRouter (Optional)

Access 300+ models through a single API. Enable for variety or specific model access.

- Get your API key at https://openrouter.ai/keys

## Available Tools

### second_opinion

Get a straightforward second opinion on any question, code, or decision.

```
Use second_opinion to review this database schema: [paste schema]
```

### challenge

Anti-sycophancy mode. The model is instructed to find weaknesses, not validate.

```
Use challenge to critique: "We should use a global singleton for database connections"
```

### code_review

Systematic directory-based code review with BLOCKER/CRITICAL/MAJOR/MINOR classifications.

```
Use code_review on directory="./src" with focus_areas=["security", "performance"]
```

### consensus

Multi-model debate where DeepSeek and Moonshot argue opposing positions, then synthesize.

```
Use consensus to debate: "GraphQL vs REST for internal microservices"
```

### review_synthesis

Full workflow: parallel reviews from both models, debate, then synthesis instructions.

```
Perform a comprehensive code review of ./myproject using review_synthesis
```

### architect_review

Review an implementation plan before coding begins. Identifies architectural risks, missing edge cases, security gaps, and over-engineering. Defaults to OpenAI if enabled.

```
Use architect_review to review this plan: [paste plan document]
```

```
Use architect_review with context="We're building a REST API for a fintech startup"
to review: [paste design document]
```

### implementation_review

Review actual code changes after implementation, optionally against the original plan. Analyzes for bugs, security issues, and quality. Defaults to OpenAI if enabled.

```
Use implementation_review on directory="./src"
```

```
Use implementation_review on directory="./src" with plan="[paste original plan]"
and save_to="./docs/reviews"
```

## Usage Examples

### Thorough Code Review Workflow

For comprehensive code reviews, use this prompt pattern with Claude Code:

```
MyProject: perform a comprehensive deep parallel code review with deepseek and kimi
using mcp server second-opinion - save resulting md files to the project folder
to the docs subfolder in md format.

After that perform Consensus debate + arbiter synthesis using same mcp server tools
with opus 4.5 compiling a final document for the final review.

First 2 tasks can be run in parallel.
```

This triggers parallel code_review calls to DeepSeek and Moonshot, then a consensus debate on findings, and finally Claude synthesizes the final review document.

### Plan-Then-Review Workflow

Use architect_review before coding and implementation_review after:

```
1. Use architect_review to review my plan: [paste plan]
2. [Make changes based on feedback]
3. Use implementation_review on directory="./src" with plan="[paste plan]"
```

### Quick Second Opinion

```
Use second_opinion to review this database schema:
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  email VARCHAR(255),
  password VARCHAR(255)
);
```

### Critical Challenge

```
Use challenge to critique this proposal: "We should use a global singleton for
database connections because it's simpler"
```

### Consensus Debate

```
Use consensus to debate: "GraphQL vs REST for our internal microservices API"
```

### Code Review with Focus Areas

```
Use code_review on directory="./src" with focus_areas=["security", "error-handling"]
and save_to="./docs/reviews"
```

## Configuration

### Changing Providers

To reconfigure which providers are enabled, run the setup wizard again:

```bash
second-opinion-mcp setup
```

Or re-register the server with specific providers:

```bash
# Auto-detect all configured providers (default)
claude mcp add -s user second-opinion -- second-opinion-mcp

# Restrict to specific providers
claude mcp add -s user second-opinion -e SECOND_OPINION_PROVIDERS="deepseek,moonshot" -- second-opinion-mcp
```

### API Key Management

Credentials are stored using platform-appropriate storage:

| Platform | Storage Location |
|----------|-----------------|
| Windows | Windows Credential Manager |
| macOS (GUI) | macOS Keychain |
| macOS (headless/SSH) | `~/.second-opinion-config` |
| Linux | `~/.second-opinion-config` |

On Linux and headless macOS, credentials are stored in `~/.second-opinion-config` with SSH-style permissions (600). This is the same security model used by SSH private keys.

OpenAI OAuth tokens are stored in `~/.second-opinion-config` under `openai_oauth` and automatically refreshed at runtime. Codex CLI tokens from `~/.codex/auth.json` are also supported as a fallback.

To update keys:

```bash
second-opinion-mcp setup
```

Or manually edit `~/.second-opinion-config` (Linux/macOS headless):

```json
{
  "credentials": {
    "deepseek": "sk-YOUR_DEEPSEEK_KEY",
    "moonshot": "YOUR_MOONSHOT_KEY",
    "openrouter": "sk-or-YOUR_OPENROUTER_KEY",
    "openai": "sk-YOUR_OPENAI_KEY"
  }
}
```

Then set permissions: `chmod 600 ~/.second-opinion-config`

## Troubleshooting

### "No API key configured" Error

Run the setup wizard again:

```bash
second-opinion-mcp setup
```

For OpenAI specifically, you can also authenticate via the setup wizard OAuth flow or Codex CLI:

```bash
# Recommended: built-in OAuth login
second-opinion-mcp setup  # Choose "Login with ChatGPT Plus (OAuth)"

# Alternative: Codex CLI
codex login
```

### Connection Timeout

Check firewall, VPN, or proxy settings. Both DeepSeek (api.deepseek.com) and Moonshot (api.moonshot.ai) must be accessible.

### Rate Limit Exceeded

Moonshot has rate limits (3 concurrent, 20 RPM at Tier 0). Wait a minute and retry, or use fast mode for non-critical queries.

### Tool Not Found in Claude

Verify registration:

```bash
claude mcp list
```

If not listed, re-register:

```bash
claude mcp add -s user second-opinion -- second-opinion-mcp
```

## Advanced Usage

### Fast Mode

Skip the thinking/reasoning phase for quicker responses:

```
Use second_opinion with fast=true to check: is this regex correct?
```

Note: Code reviews and implementation reviews always use full thinking mode regardless of this setting.

### Include Reasoning

See the model's chain-of-thought:

```
Use second_opinion with include_reasoning=true to analyze this algorithm
```

### Focus Areas for Reviews

```
Use code_review with focus_areas=["security", "error-handling", "performance"]
```

### Save Review Output

```
Use code_review on directory="./src" with save_to="./docs/reviews"
```

## Updating

The server checks for updates on startup and notifies you if a new version is available.

To update manually:

```bash
pipx upgrade second-opinion-mcp
```

Or reinstall:

```bash
pipx uninstall second-opinion-mcp
pipx install second-opinion-mcp
```

Your API keys are preserved in the system keyring across updates.

## Uninstalling

```bash
# Remove from Claude
claude mcp remove second-opinion

# Optional: remove stored API keys BEFORE uninstalling (requires pipx venv Python)
SOPYTHON=~/.local/share/pipx/venvs/second-opinion-mcp/bin/python3
$SOPYTHON -c "import keyring; keyring.delete_password('second-opinion', 'deepseek')"
$SOPYTHON -c "import keyring; keyring.delete_password('second-opinion', 'moonshot')"
$SOPYTHON -c "import keyring; keyring.delete_password('second-opinion', 'openrouter')"
$SOPYTHON -c "import keyring; keyring.delete_password('second-opinion', 'openai')"

# Uninstall package
pipx uninstall second-opinion-mcp
```

## Security

API keys are stored in your OS keyring, not in environment variables or config files. OpenAI OAuth tokens are stored in `~/.second-opinion-config` and refreshed automatically. Codex CLI tokens from `~/.codex/auth.json` are also supported as a fallback. The code review tool:

- Skips `.env` files, credentials, SSH keys, and certificates
- Validates directories against allowed roots
- Detects symlinks to prevent traversal attacks
- Limits content size to prevent memory exhaustion

## Cost Estimates

Per operation (typical usage):

| Tool | Approximate Cost |
|------|------------------|
| second_opinion / challenge | ~$0.001 |
| code_review | ~$0.01-0.05 |
| consensus (2 rounds) | ~$0.004-0.010 |
| review_synthesis | ~$0.02-0.10 |
| architect_review | ~$0.01-0.03 |
| implementation_review | ~$0.01-0.05 |

OpenAI costs are higher per token than DeepSeek/Moonshot. Using OAuth login with ChatGPT Plus provides free access (subject to rate limits). OAuth flow ported from OpenClaw (MIT, github.com/openclaw/openclaw).

## License

MIT License. See LICENSE file.

## Links

- [GitHub Repository](https://github.com/MarvinFS/second-opinion-mcp)
- [Issue Tracker](https://github.com/MarvinFS/second-opinion-mcp/issues)
- [Changelog](https://github.com/MarvinFS/second-opinion-mcp/blob/main/docs/CHANGELOG.md)
