AI agents invoke fix_code_tool to trigger actions in FastMCP Boilerplate. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool processes and transforms code, likely executing analysis and generating modified code output. 'Fix and refactor' implies it actively modifies/rewrites code, which could introduce unintended changes. While the description is minimal, refactoring code is at least a Write-level operation, and if it can execute the code to test fixes, it rises to Execute.
From the tool's definition Fix and refactor provided code
Documented attack patterns abuse exactly the kind of access fix_code_tool gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and FastMCP Boilerplate, and nothing reaches the server without passing your rules. This is the rule we recommend for fix_code_tool:
{
"version": "1",
"default": "deny",
"tools": {
"fix_code_tool": {
"limits": [
{
"counter": "fix_code_tool_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}fix_code_tool stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Fix and refactor provided code. It is categorised as a Execute tool in the FastMCP Boilerplate MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the FastMCP Boilerplate MCP server in PolicyLayer and add a rule for fix_code_tool: 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 FastMCP Boilerplate. Nothing to install.
fix_code_tool is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the fix_code_tool 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.
Set action: deny in the PolicyLayer policy for fix_code_tool. 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.
fix_code_tool is provided by the FastMCP Boilerplate MCP server (rainer85ah/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from FastMCP Boilerplate, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
16 FastMCP Boilerplate tools catalogued and risk-classified — across an index of 43,000+ MCP servers.