MySQL MCP: using password NO (MYSQL_* vars set in shell, not client env block)

TL;DR: You exported MYSQL_PASS in your terminal, but the MCP server never saw it. MCP clients launch servers with a clean environment. Put every MYSQL_* variable in the client config's env block instead.

ER_ACCESS_DENIED_ERROR: Access denied for user 'appuser'@'host' (using password value NO)

(The tell is using password value NO even though you set one.)

Fix it

1. Move all five variables into the server's env block in your client config:

{
  "mcpServers": {
    "mysql": {
      "command": "npx",
      "args": ["-y", "mcp-server-mysql"],
      "env": {
        "MYSQL_HOST": "YOUR_MYSQL_HOST",
        "MYSQL_PORT": "3306",
        "MYSQL_USER": "appuser",
        "MYSQL_PASS": "yourpassword",
        "MYSQL_DB": "mydb"
      }
    }
  }
}

2. Fully quit and restart the client. Servers spawn at client launch.

   Expected: (using password value YES) in any subsequent error, and with correct values, a working connection.

When to use this

• The error says using password value NO but you definitely set a password somewhere.
• echo $MYSQL_PASS works in your terminal but the server acts like it is empty.
• You are on Windows, where GUI-launched servers do not inherit terminal env at all.

When NOT to use this

• The error says using password value YES and still denies access. The value is reaching the server but is wrong.
• The error is ECONNREFUSED or Unknown database. Those are host and database problems.

Compatibility

• benborla/mcp-server-mysql and any env-configured MCP database server.
• Claude Desktop, Claude Code, Cursor, Windsurf.

Why it happens

export affects your shell and its children. The MCP client is not your shell's child (especially GUI apps), so it never sees those variables, and the server it spawns inherits the client's clean environment. The env block exists precisely to bridge this gap.

Edge cases

• JSON-escape backslashes and double quotes inside passwords in the config file.
• If you use a secrets manager or 1Password-style env injection, make sure the injection applies to the client process, not just your terminal.
• After moving the vars, unset the shell exports to avoid confusion about which value is live.

The benborla/mcp-server-mysql server reads its configuration (MYSQLHOST, MYSQLPORT, MYSQLUSER, MYSQLPASS, MYSQLDB) from environment variables. MCP clients launch stdio servers with a clean environment that does not inherit interactive shell exports, so variables set via export in a terminal are not visible to the server process. The reliable channel is the env block in the MCP client configuration (claudedesktop_config.json, .mcp.json). This is the same documented behavior as other env-configured MCP database servers.