MySQL MCP: ECONNREFUSED (MySQL not running or wrong MYSQL_HOST/PORT)

TL;DR: ECONNREFUSED means nothing is listening where the MCP server is looking. Start MySQL, then make sure MYSQL_HOST and MYSQL_PORT in the client config match where it actually listens. The defaults (YOUR_HOST:3306) are wrong for Docker and remote setups.

Error: connect ECONNREFUSED the loopback address:3306

Fix it

1. Check MySQL is running:

# Linux
sudo systemctl status mysql
# macOS (Homebrew)
brew services list
# Docker
docker ps | grep mysql

2. Check what it listens on:

sudo netstat -tlnp | grep 3306

Expected: a line showing mysqld on 3306 (or your configured port).

3. Set the real address in the client config env block. Docker on the host: host.YOUR_HOST. Docker Compose service: the service name. Remote: the hostname or IP.

{
  "env": {
    "MYSQL_HOST": "host.YOUR_HOST",
    "MYSQL_PORT": "3306"
  }
}

4. Restart the MCP client.

   Expected: the refused error is gone. Next failure, if any, will be auth, which is progress.

When to use this

• The error is ECONNREFUSED mentioning the MySQL host and port.
• mysql -h [host] from a terminal also fails to connect.

When NOT to use this

• The error is ER_ACCESS_DENIED_ERROR. The server is reachable; credentials are wrong.
• The error is a timeout (ETIMEDOUT). That is firewall or routing, not a refused connection.

Compatibility

• benborla/mcp-server-mysql.
• MySQL 5.7, 8.x, MariaDB, in Docker or on the host.

Why it happens

Connection refused is the OS telling you the SYN packet arrived but no process accepted it. Either MySQL is down, or it is up but bound to a different interface or port than the config says. MCP defaults assume a local MySQL on 3306, which breaks the moment MySQL lives in Docker or on another machine.

Edge cases

• MySQL in Docker without a published port is unreachable from the host. Add -p 3306:3306.
• bind-address = the loopback address in my.cnf blocks remote connections even when the port is open. Set it to the all-interfaces address for remote access (with proper grants).
• Skip-networking enabled means TCP is off entirely. The MCP server needs TCP; use a socket only if the server supports it.

ECONNREFUSED is the standard TCP connection-refused error when the MySQL server is not running or not listening at the configured host and port, documented in MySQL troubleshooting guides with the fix of starting the MySQL service and verifying the host and port. The benborla/mcp-server-mysql server reads MYSQLHOST and MYSQLPORT from the environment, defaulting to YOUR_HOST:3306, so a MySQL running elsewhere or on a different port produces this exact error. Source: https://github.com/benborla/mcp-server-mysql