Parse and explain cron expressions
Risk signalsAccepts freeform code/query input (expression)
Part of the Ucd server.
Free to start. No card required.
AI agents invoke build-cron to trigger processes or run actions in Ucd. Execute operations can have side effects beyond the immediate call -- triggering builds, sending notifications, or starting workflows. Rate limits and argument validation are essential to prevent runaway execution.
build-cron can trigger processes with real-world consequences. An uncontrolled agent might start dozens of builds, send mass notifications, or kick off expensive compute jobs. PolicyLayer enforces rate limits and validates arguments to keep execution within safe bounds.
Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.
{
"version": "1",
"default": "deny",
"tools": {
"build-cron": {
"limits": [
{
"counter": "build-cron_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}See the full Ucd policy for all 21 tools.
These attack patterns abuse exactly the kind of access build-cron gives an agent. Each links to the full case and the policy that stops it:
Other execute tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Parse and explain cron expressions. It is categorised as a Execute tool in the Ucd MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Ucd MCP server in PolicyLayer and add a rule for build-cron: 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 Ucd. Nothing to install.
build-cron 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 build-cron 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 build-cron. 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.
build-cron is provided by the Ucd MCP server (underground-district/ucd-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 21 Ucd tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.