Bug: --readonly False flag doesn't work - MySQL MCP server is always read-only

[KevinZhao]

Bug Description

The --readonly False flag in mysql-mcp-server does not work. The server is always in read-only mode regardless of the --readonly parameter value.

Root Cause

In src/mysql-mcp-server/awslabs/mysql_mcp_server/server.py, the --readonly argument is defined as a string via argparse:

parser.add_argument(
    '--readonly', required=True, help='Enforce NL to SQL to only allow readonly sql statement'
)

It is then passed to DBConnectionSingleton.initialize() as:

readonly=args.readonly.lower(),  # "False".lower() → "false" (still a string!)

The DBConnectionSingleton type-hints the parameter as bool, but Python does not enforce type annotations at runtime. The string "false" is stored directly in AbstractDBConnection._readonly.

In Python, any non-empty string is truthy:

>>> bool("false")
True
>>> bool("False")
True

So db_connection.readonly_query always returns True, and all mutating queries are rejected.

Steps to Reproduce

1. Configure MySQL MCP server with --readonly False
2. Attempt any write query (INSERT, UPDATE, DELETE, CREATE TABLE, etc.)
3. Receive error: "Your MCP tool only allows readonly query. If you want to write, change the MCP configuration per README.md"

Affected Version

awslabs.mysql-mcp-server v1.0.15 (latest as of 2025-02-08)

Suggested Fix

In server.py, convert the string to an actual boolean:

# Before (line ~189 and ~215):
readonly=args.readonly.lower(),

# After:
readonly=(args.readonly.lower() == 'true'),

Or better, use argparse's built-in boolean handling:

parser.add_argument(
    '--readonly',
    required=True,
    type=lambda x: x.lower() == 'true',
    help='Enforce NL to SQL to only allow readonly sql statement'
)

Environment

• OS: Amazon Linux 2023 (aarch64)
• Python: 3.10
• Package: awslabs.mysql-mcp-server 1.0.15
• Client: Claude Code 2.1.37