second-opinion-mcp

Leia em portugues: Portugues

MCP server that gives any AI coding tool a structured second opinion from another AI provider.

Why This Exists

AI coding assistants hallucinate, miss bugs, and give outdated advice. This server lets them cross-check answers with a different AI provider and get back a machine-readable verdict they can act on. Not chat, not markdown -- fixed JSON schemas with enums (YES/NO, PASS/FAIL), confidence levels, and evidence arrays, all validated with Zod.

Providers

Provider	Env Key	Default Model	Pricing
Gemini	GEMINI_API_KEY	gemini-2.5-flash	Free tier available (may require billing enabled on Google Cloud). Paid plans for higher limits
OpenAI	OPENAI_API_KEY	gpt-4.1-mini	Pay-as-you-go (requires billing)
Groq	GROQ_API_KEY	llama-3.3-70b-versatile	Free tier available, paid plans for higher limits
DeepSeek	DEEPSEEK_API_KEY	deepseek-chat	Pay-as-you-go (requires billing)

Set one API key and the server auto-detects the provider. Detection order: Gemini > OpenAI > Groq > DeepSeek.

Quick Start

Claude Code (one command)

# With Gemini (free tier)
claude mcp add second-opinion -s user -e GEMINI_API_KEY=your-key -- npx @mrssoftwares/second-opinion-mcp

# With OpenAI
claude mcp add second-opinion -s user -e OPENAI_API_KEY=your-key -- npx @mrssoftwares/second-opinion-mcp

# With Groq (free tier)
claude mcp add second-opinion -s user -e GROQ_API_KEY=your-key -- npx @mrssoftwares/second-opinion-mcp

# With DeepSeek
claude mcp add second-opinion -s user -e DEEPSEEK_API_KEY=your-key -- npx @mrssoftwares/second-opinion-mcp

Other MCP Clients (JSON config)

{
  "mcpServers": {
    "second-opinion": {
      "command": "npx",
      "args": ["@mrssoftwares/second-opinion-mcp"],
      "env": {
        "GEMINI_API_KEY": "your-key-here"
      }
    }
  }
}

From Source

git clone https://github.com/mauricioreiss/second-opinion-mcp.git
cd second-opinion-mcp
npm install && npm run build

Tools

second_opinion_ask

Ask a technical question. Returns a verdict, not a wall of text.

Parameter	Type	Required	Description
question	string	yes	The technical question
context	string	no	Additional context

{
  "verdict": "NO",
  "confidence": "HIGH",
  "answer": "Usar eval() para parsing de JSON e inseguro. Use JSON.parse().",
  "evidence": [
    "eval() executa codigo arbitrario, permitindo injecao de codigo",
    "JSON.parse() rejeita JSON invalido sem executar codigo"
  ],
  "provider": "gemini",
  "model": "gemini-2.5-flash"
}

Verdict: YES | NO | PARTIAL | UNCERTAIN. Confidence: HIGH | MEDIUM | LOW.

second_opinion_review

Code review with structured findings per criterion.

Parameter	Type	Required	Description
code	string	yes	Code or diff to review
language	string	no	Language (auto-detected if omitted)
focus	string[]	no	Review criteria (default: security, performance, correctness, error-handling)

{
  "verdict": "FAIL",
  "score": 3,
  "criteria": [
    {
      "name": "security",
      "status": "FAIL",
      "findings": [
        {
          "severity": "HIGH",
          "line": 5,
          "issue": "SQL injection via string interpolation",
          "fix": "Use parameterized queries: db.query('SELECT * FROM users WHERE id = $1', [id])"
        }
      ]
    }
  ],
  "summary": "Vulnerabilidade critica de SQL injection encontrada.",
  "provider": "gemini",
  "model": "gemini-2.5-flash"
}

Verdict: PASS | FAIL | WARNING. Score: 1-10. Finding severity: HIGH | MEDIUM | LOW. Line can be null.

second_opinion_verify

Fact-check a technical claim.

Parameter	Type	Required	Description
claim	string	yes	The claim to verify
context	string	no	Additional context

{
  "verdict": "PARTIAL",
  "confidence": "MEDIUM",
  "explanation": "Redis WATCH monitora chaves, mas nao garante isolamento total como locks tradicionais.",
  "caveats": [
    "WATCH usa optimistic locking, nao bloqueia outros clientes",
    "A transacao precisa ser re-tentada manualmente apos abort"
  ],
  "docs_to_check": [
    "Redis WATCH command docs",
    "Redis transactions documentation"
  ],
  "provider": "gemini",
  "model": "gemini-2.5-flash"
}

Verdict: YES | NO | PARTIAL | OUTDATED | UNCERTAIN. Confidence: HIGH | MEDIUM | LOW.

second_opinion_compare

Compare two approaches with per-criterion breakdown.

Parameter	Type	Required	Description
approach_a	{name, description}	yes	First approach
approach_b	{name, description}	yes	Second approach
criteria	string[]	no	Comparison criteria (default: performance, maintainability, complexity, scalability)
context	string	yes	Context for the comparison

{
  "winner": "APPROACH_A",
  "confidence": "HIGH",
  "comparison": [
    {
      "criterion": "performance",
      "winner": "TIE",
      "reason": "Ambos operam em microsegundos para operacoes simples de key-value"
    },
    {
      "criterion": "features",
      "winner": "APPROACH_A",
      "reason": "Redis tem TTL nativo e pub/sub, facilitando gerenciamento de sessoes"
    }
  ],
  "recommendation": "Redis e a melhor escolha para sessoes. TTL nativo elimina logica de expiracao manual.",
  "provider": "gemini",
  "model": "gemini-2.5-flash"
}

Winner: APPROACH_A | APPROACH_B | TIE | DEPENDS. Per-criterion winner: APPROACH_A | APPROACH_B | TIE.

Recommended Usage

Add this to your project's CLAUDE.md (or equivalent AI instructions file):

Before committing critical code (auth, payments, sensitive data),
use the `second_opinion_review` tool to get an external review.
If the verdict is FAIL or score < 6, fix the issues before proceeding.

This is not a chat — it is a structured review with JSON output, numeric score, findings per criterion, and fix suggestions. It integrates into any workflow: CI pipelines, pre-commit hooks, or manual checks.

How It Works

• Your AI tool calls one of the 4 MCP tools with structured input
• The server builds a prompt that forces JSON-only output for the configured provider (Gemini, OpenAI, Groq, or DeepSeek)
• The response goes through a parse pipeline: JSON.parse -> retry with correction prompt -> regex extraction
• The parsed object is validated against a Zod schema. If it passes, the structured verdict is returned to the caller

Every response follows a fixed schema. No markdown, no chat, no surprises.

Configuration

Variable	Description
GEMINI_API_KEY	Google Gemini API key
OPENAI_API_KEY	OpenAI API key
GROQ_API_KEY	Groq API key
DEEPSEEK_API_KEY	DeepSeek API key
SECOND_OPINION_PROVIDER	Force a specific provider (skips auto-detection)
SECOND_OPINION_MODEL	Force a specific model (overrides provider default)

Only one API key is required. See .env.example for details and links to get each key.

Limitations

• Responses are in Brazilian Portuguese (pt-BR) by default
• One provider at a time (no multi-provider consensus)
• 30-second timeout per request
• Rate limits depend on your provider plan (free tiers have lower limits; paid plans remove most restrictions)
• Gemini free tier may return 503 errors if billing is not enabled on your Google Cloud project or if you exceed the free quota. If this happens, enable billing at https://console.cloud.google.com/billing or switch to another provider
• LLM responses are non-deterministic; the same input may produce different verdicts across calls

License

MIT