Parse, explain, and validate cron expressions via cron-forge-mcp (npx)

cron-forge-mcp — parse, explain, and validate cron expressions via MCP

Package: [email protected] (npm) Transport: stdio via npx -y cron-forge-mcp Auth: none — zero config Tools: 3 — explain_cron, next_cron_runs, validate_cron

MCP config

{
  "mcpServers": {
    "cron": {
      "command": "npx",
      "args": ["-y", "cron-forge-mcp"]
    }
  }
}

Tool schemas (from tools/list)

Verified traces

1. explain_cron — human-readable explanation of business-hours schedule

→ tools/call explain_cron {expression: "*/15 9-17 * * 1-5"}
← Cron: */15 9-17 * * 1-5
  Schedule:
  - Minute: every 15 minutes
  - Hour: hours 9-17
  - Day of month: every day
  - Month: every month
  - Day of week: weekdays 1-5

2. next_cron_runs — next 5 Sunday midnight runs

→ tools/call next_cron_runs {expression: "0 0 * * 0", count: 5}
← Next 5 runs:
  2026-06-13T21:00:00.000Z
  2026-06-20T21:00:00.000Z
  2026-06-27T21:00:00.000Z
  2026-07-04T21:00:00.000Z
  2026-07-11T21:00:00.000Z

Note: times are offset from midnight UTC — the server appears to apply a local timezone offset but labels results with Z (UTC). Consumers should be aware the "next run" times may not be pure UTC.

3. validate_cron — validation of invalid expression

→ tools/call validate_cron {expression: "0 25 * * *"}
← Cron: 0 25 * * *
  ✓ Minute (0-59): 0
  ✓ Hour (0-23): 25
  ✓ Day of month (1-31): *
  ✓ Month (1-12): *
  ✓ Day of week (0-6): *

BUG: validate_cron does not range-check field values

validate_cron reports "✓ Hour (0-23): 25" — hour 25 is clearly outside the valid 0–23 range, yet the server marks it as valid. The validator only checks structural syntax (correct number of fields, parseable tokens) but does NOT verify that values fall within each field's documented range. Do not rely on validate_cron for semantic validation. It's a parser, not a validator — the label is misleading.

Summary

All 3 tools responded. explain_cron and next_cron_runs produce useful output. validate_cron has a significant false-positive bug where out-of-range values pass validation.