// MCP TOOL REFERENCE

build-cron

Parse and explain cron expressions

Accepts freeform code/query input (expression)

Part of the Ucd MCP server. Enforce policies on this tool with Intercept, the open-source MCP proxy.

underground-district/ucd-mcp Execute Risk 4/5

// WHEN AI AGENTS USE THIS TOOL

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.

// WHY ENFORCE A POLICY ON BUILD-CRON

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. Intercept enforces rate limits and validates arguments to keep execution within safe bounds.

// RECOMMENDED POLICY

Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.

underground-district-ucd-mcp.yaml

tools:
  build-cron:
    rules:
      - action: allow
        rate_limit:
          max: 10
          window: 60
        validate:
          required_args: true

See the full Ucd policy for all 19 tools.

// DETAILS

Tool Name build-cron

Category Execute

MCP Server Ucd MCP Server

Risk Level High

// MORE UCD TOOLS

Execute agent-mesh Write agent-identity Write convert-eth-units Write convert-timestamp Write decode-base64 Write decode-jwt Write encode-base64 Write encode-url

View all 19 tools →

// WHAT CAN GO WRONG

Agents calling execute-class tools like build-cron have been implicated in these attack patterns. Read the full case and prevention policy for each:

Browse the full MCP Attack Database →

// OTHER EXECUTE TOOLS ACROSS MCP SERVERS

Other tools in the Execute risk category across the catalogue. The same policy patterns (rate-limit, validate) apply to each.

Agent Passport System — Cryptographic Identity for AI Agents commerce_preflight Agent Passport System — Cryptographic Identity for AI Agents execute_with_context Agent Passport System — Cryptographic Identity for AI Agents gateway_execute_approval Agent Passport System — Cryptographic Identity for AI Agents governance_360 Agent Passport System — Cryptographic Identity for AI Agents parse_governance_block_html AgentClear — API Marketplace for AI Agents call_service

// IN CONTEXT OF HIGH RISK

build-cron is one of the high-risk operations in Ucd. For the full severity-focused view — only the high-risk tools with their recommended policies — see the breakdown for this server, or browse all high-risk tools across every MCP server.

// RELATED READING

// FAQ

What does the build-cron tool do? +

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.

How do I enforce a policy on build-cron? +

Add a rule in your Intercept YAML policy under the tools section for build-cron. You can allow, deny, rate-limit, or validate arguments. Then run Intercept as a proxy in front of the Ucd MCP server.

What risk level is build-cron? +

build-cron is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit build-cron? +

Yes. Add a rate_limit block to the build-cron rule in your Intercept 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 build-cron completely? +

Set action: deny in the Intercept 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.

What MCP server provides build-cron? +

build-cron is provided by the Ucd MCP server (underground-district/ucd-mcp). Intercept sits as a proxy in front of this server to enforce policies before tool calls reach the server.

build-cron

Enforce policies on Ucd