write_query · MySQL- MCP: Risk & Policy

WHAT IT DOES

What write_query does on MySQL-MCP

AI agents use write_query to create or update resources in MySQL-MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MySQL-MCP environment.

WHY IT NEEDS A POLICY

Why write_query needs a policy

The tool's explicit purpose is to modify data through INSERT (create), UPDATE (modify), and DELETE (remove) operations. While DELETE is destructive in nature, the tool's primary design intent covers all three DML write operations. INSERT and UPDATE are clearly Write category operations.

From the tool's definition Tool description states 'Execute an INSERT, UPDATE, or DELETE query'. INSERT and UPDATE are reversible write operations; DELETE is listed but the tool is categorized as Write rather than Destructive because DELETE via this tool can potentially be undone with…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

write_query Rate-limited

write_query stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "write_query": {
      "limits": [
        {
          "counter": "write_query_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches MySQL-MCP, so you can run agents against it safely.

FAQ

Questions about write_query

What does the write_query tool do? +

Execute an INSERT, UPDATE, or DELETE query. It is categorised as a Write tool in the MySQL-MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_query? +

Register the MySQL- MCP server in PolicyLayer and add a rule for write_query: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches MySQL-MCP. Nothing to install.

What risk level is write_query? +

write_query is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit write_query? +

Yes. Add a rate_limit block to the write_query rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block write_query completely? +

Set action: deny in the PolicyLayer policy for write_query. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides write_query? +

write_query is provided by the MySQL- MCP server (zajtools/zaj-mysql-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.