preflight-tools 0.1.1

Reference validators for autonomous systems protocols: MCP, A2A, ACE, OCC/OCS/OCP

Preflight Tools

Reference validators for autonomous systems protocols: MCP, A2A, ACE, OCC/OCS/OCP

Overview

Preflight Tools provides reference implementations for protocol compliance validation across autonomous agent ecosystems. These validators catch common integration issues before deployment, saving hours of debugging.

Supported Protocols

• MCP (Model Context Protocol) - Anthropic's protocol for LLM tool integration
• A2A (Agent-to-Agent) - Peer communication protocol for autonomous agents
• ACE (Autonomic Compliance Ecosystem) - Platform orchestration standards
• OCC/OCS/OCP - (Coming soon) Observability, compliance, and policy protocols

Installation

# Via pip
pip install preflight-tools

# Via Poetry
poetry add preflight-tools

# From source
git clone https://github.com/syzygysys/preflight-tools.git
cd preflight-tools
poetry install

Quick Start

MCP Validation

Validate your MCP server implementation against the specification:

# Validate a tools definition file
mcp-preflight-check validate path/to/tools.py

# Test a running server
mcp-preflight-check test http://localhost:8000

# Full report with verbose output
mcp-preflight-check validate --verbose path/to/tools.py

Example output:

✅ Tool names: All valid [a-zA-Z0-9_-]
✅ Properties schemas: All using objects {}
✅ Content wrappers: All responses properly wrapped
✅ Notification handling: Correctly implemented
✅ JSON-RPC structure: All responses include required fields
❌ Stdout pollution: Found 3 print statements that will break stdio transport

Fix suggestions:
  Line 42: Remove print() statement
  Line 89: Use logging instead of print()
  Line 134: Redirect to stderr

A2A Validation

(Coming soon) Validate Agent-to-Agent protocol implementations:

a2a-preflight-check validate path/to/agent_config.yml

The Six Critical MCP Fixes

This validator is built from real-world debugging of LAP::CORE's MCP integration. See the full story: Debugging the Bridge

1. Tool Name Pattern

Problem: Tool names with dots fail Zod validation
Rule: Must match ^[a-zA-Z0-9_-]{1,64}$

# ❌ FAILS
{"name": "lap.health.ping"}

# ✅ PASSES
{"name": "lap_health_ping"}

2. Properties Schema Type

Problem: Empty properties as [] instead of {}
Rule: JSON Schema requires properties to be an object

# ❌ FAILS
{
    "inputSchema": {
        "type": "object",
        "properties": []  # Wrong type
    }
}

# ✅ PASSES
{
    "inputSchema": {
        "type": "object",
        "properties": {}  # Correct type
    }
}

3. Content Wrapper Structure

Problem: Returning raw data instead of MCP content structure
Rule: All responses must be wrapped

# ❌ FAILS
return {"status": "ok", "value": 42}

# ✅ PASSES
return {
    "content": [{
        "type": "text",
        "text": json.dumps({"status": "ok", "value": 42})
    }]
}

4. Notification Handling

Problem: Returning errors for notification requests (no id field)
Rule: Notifications don't expect responses

# ❌ FAILS
async def dispatch(self, request: dict) -> str:
    method = request.get("method")
    if method not in self.handlers:
        return json.dumps({"error": "unknown method"})

# ✅ PASSES
async def dispatch(self, request: dict) -> str:
    # Check if this is a notification (no "id" field)
    if "id" not in request:
        return ""  # Silent success
    
    method = request.get("method")
    # ... handle request-response

5. Stdout Pollution

Problem: Any output to stdout breaks JSON-RPC stdio transport
Rule: Redirect stderr early, never use print()

# ❌ FAILS - stderr goes to stdout
poetry run mcp-server 2>> /tmp/debug.log

# ✅ PASSES - redirect before Python starts
exec 2>/tmp/debug.log; poetry run mcp-server

In code:

# ❌ NEVER
print("Debug message")

# ✅ ALWAYS
import logging
logging.error("Debug message")  # Goes to stderr

6. JSON-RPC Response Structure

Problem: Using exclude_none=True removes required fields when they're None
Rule: JSON-RPC 2.0 requires id and jsonrpc in every response

# ❌ FAILS - removes 'id' when it's None
class JsonRpcResponse(BaseModel):
    jsonrpc: str = "2.0"
    id: Optional[Any] = None
    result: Optional[Any] = None
    error: Optional[Dict[str, Any]] = None
    
    def json(self, **kwargs):
        return self.model_dump_json(exclude_none=True, **kwargs)

# ✅ PASSES - keeps required fields
class JsonRpcResponse(BaseModel):
    jsonrpc: str = "2.0"
    id: Optional[Any] = None
    result: Optional[Any] = None
    error: Optional[Dict[str, Any]] = None
    
    def json(self, **kwargs):
        data = self.model_dump()
        # Keep id and jsonrpc always, only exclude result/error conditionally
        if data.get('error') is not None:
            data.pop('result', None)
        elif data.get('result') is not None:
            data.pop('error', None)
        return json.dumps(data)

API Usage

Python API

from preflight_tools.mcp import MCPValidator

validator = MCPValidator()

# Validate a tools file
results = validator.validate_file("path/to/tools.py")

for issue in results.issues:
    print(f"{issue.severity}: {issue.message}")
    print(f"  Fix: {issue.suggestion}")

# Test a running server
results = validator.test_server("http://localhost:8000")
print(f"Protocol version: {results.protocol_version}")
print(f"Tools found: {len(results.tools)}")

Configuration

Create a .preflight.toml in your project root:

[mcp]
strict = true  # Fail on warnings
ignore = ["stdout-pollution"]  # Skip specific checks

[a2a]
version = "0.1.0"
require_auth = true

Development

# Clone and setup
git clone https://github.com/syzygysys/preflight-tools.git
cd preflight-tools
poetry install

# Run tests
poetry run pytest

# Run validator on itself
poetry run mcp-preflight-check validate src/

# Format and lint
poetry run black src/ tests/
poetry run ruff check src/ tests/
poetry run mypy src/

Architecture

preflight-tools/
├── src/preflight_tools/
│   ├── mcp/              # MCP validation
│   │   ├── validator.py  # Core validation logic
│   │   ├── checks.py     # Individual check implementations
│   │   └── cli.py        # Command-line interface
│   ├── a2a/              # A2A validation (coming soon)
│   └── common/           # Shared utilities
├── tests/
│   ├── test_mcp.py
│   └── fixtures/         # Test cases
└── docs/
    └── protocols/        # Protocol specs

Contributing

We welcome contributions! This is a reference implementation for the community.

1. Fork the repo
2. Create a feature branch
3. Add tests for new validators
4. Submit a PR with clear description

See CONTRIBUTING.md for details.

Related Projects

• LAP::CORE - LAPI orchestration platform
• ACE Framework - Autonomic Compliance Ecosystem
• MCP Specification - Official MCP docs

References

• Log 14: Debugging the Bridge - The debugging session that inspired this tool
• MCP GitHub Issues - Report MCP bugs here
• SyzygySys Architecture Notebook - More technical deep-dives

License

Apache License 2.0 - See LICENSE for details.

Copyright 2025 SyzygySys

Support

• Issues: GitHub Issues
• Discussions: GitHub Discussions
• Email: [e-mail]

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