cron-mcp

An MCP (Model Context Protocol) server that lets AI coding agents — Claude, Cursor, Copilot, Cline — parse, validate, explain, and preview cron expressions.

Built to catch silent cron bugs (impossible schedules, OR-semantics gotchas, midnight spikes) before a job is deployed — a class of mistake that's easy to make and hard to notice until a critical job silently fails to fire.

Why

Cron expressions are deceptively tricky. Common silent failures:

• 0 0 30 2 * → never runs (February has no 30th). Syntactically valid, semantically dead.
• 0 0 1,15 * 1 → fires on the 1st OR 15th OR Monday, not "the 1st and 15th if Monday" (the classic dom+dow OR-semantics trap).
• */7 * * * * → uneven step; intervals drift (:00, :07, :14, …, :56, :00 — not "every 7 minutes" cleanly).
• 0 0 * * * → midnight spike; every job in the system competes at 00:00.

cron-mcp surfaces these as warnings, observations, and suggestions that the AI agent can act on — before you ship the schedule.

Tools exposed

| Tool | Description | |------|-------------| | parse_cron | Parse a cron expression → plain-English description of when it fires. Supports 5-field standard cron + L (last), W (nearest weekday), # (nth weekday), named months/days. | | validate_cron | Deep validation: impossible schedules, OR-semantics, midnight spikes, uneven steps, leap-year edges, frequency estimate (~runs/year). | | next_runs | Compute the next N fire times as ISO-8601 + relative offsets. | | cron_presets | Library of common, proven schedules (every 5 min, hourly, weekdays 9am, monthly, quarterly, …). |

Install

npm install -g cron-mcp-server

Configure

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or the equivalent on your OS:

{
  "mcpServers": {
    "cron": {
      "command": "cron-mcp-server",
      "args": []
    }
  }
}

Cursor

Add to .cursor/mcp.json (or ~/.cursor/mcp.json for global):

{
  "mcpServers": {
    "cron": {
      "command": "cron-mcp-server"
    }
  }
}

VS Code (Copilot)

{
  "mcp.servers": {
    "cron": {
      "type": "stdio",
      "command": "cron-mcp-server"
    }
  }
}

Direct (no install)

npx cron-mcp-server

Example usage

Once connected, just ask the agent in natural language:

• "Validate this cron: 0 0 30 2 *"
• "When does */5 * * * * next fire?"
• "Give me a cron for every weekday at 9am"
• "Is there anything risky about 0 0 1,15 * 1?"

The agent calls the tools and returns structured, actionable results.

Engine

The cron engine is battle-tested: 638 lines, zero dependencies, originally extracted from a browser-based cron generator and hardened with 69 unit tests. This MCP server is a thin tool wrapper around it.

License

MIT © takeaseatventure