The Problem
MCP servers fail to connect with cryptic errors: 404, 'Failed to connect', or tools silently not loading. Developers spend hours guessing instead of following a systematic debug path. Common causes: transport mismatch (HTTP vs stdio), missing URL suffix, wrong auth header, server not running.
The Scavio Solution
Follow a four-step checklist: (1) Verify transport type matches between server and client config. (2) Test the URL directly with curl. (3) Confirm the API key header name and value. (4) Check server logs for startup errors. For hosted servers, the URL format is the most common issue. For local servers, process management is the bottleneck.
Before
Before the checklist, a developer spent 2 hours debugging a BetterStack MCP connection to Claude Code. Tried reinstalling Claude Code, regenerating API keys, and restarting the computer. The actual issue was a missing /mcp path suffix in the URL.
After
After following the checklist, MCP connection issues resolve in 15 minutes. Step 1: transport check passes (HTTP). Step 2: curl to the URL returns 404 -- immediately identifies the path issue. Fix the URL, re-test with curl, connection succeeds. Documented fix prevents recurrence.
Who It Is For
Developers struggling with MCP server connections in Claude Code, Cursor, VS Code, or Windsurf who need a systematic approach instead of trial-and-error.
Key Benefits
- 15-minute resolution for most MCP connection issues
- Covers all four common failure modes systematically
- curl-based verification isolates client vs server issues
- Works for hosted MCP (Scavio, Tavily) and local servers
- Checklist prevents hours of guesswork debugging
Python Example
import requests, subprocess, json
def debug_mcp_connection(url: str, api_key: str) -> dict:
"""Systematic MCP connection debug checklist."""
results = {'url': url, 'checks': []}
# Check 1: URL format
if not url.endswith('/mcp'):
results['checks'].append({'check': 'url_format', 'status': 'warning',
'message': 'URL may need /mcp suffix'})
else:
results['checks'].append({'check': 'url_format', 'status': 'pass'})
# Check 2: Server reachable
try:
r = requests.get(url, headers={'x-api-key': api_key}, timeout=10)
results['checks'].append({'check': 'reachable', 'status': 'pass',
'http_code': r.status_code})
except Exception as e:
results['checks'].append({'check': 'reachable', 'status': 'fail',
'error': str(e)})
return results
result = debug_mcp_connection('https://mcp.scavio.dev/mcp', 'test-key')
print(json.dumps(result, indent=2))JavaScript Example
async function debugMcpConnection(url, apiKey) {
const checks = [];
if (!url.endsWith('/mcp')) {
checks.push({ check: 'url_format', status: 'warning', message: 'URL may need /mcp suffix' });
} else checks.push({ check: 'url_format', status: 'pass' });
try {
const r = await fetch(url, { headers: { 'x-api-key': apiKey } });
checks.push({ check: 'reachable', status: r.ok ? 'pass' : 'fail', httpCode: r.status });
} catch (e) {
checks.push({ check: 'reachable', status: 'fail', error: e.message });
}
return { url, checks };
}
const result = await debugMcpConnection('https://mcp.scavio.dev/mcp', 'test-key');
console.log(JSON.stringify(result, null, 2));Platforms Used
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