cron-explainer

A tiny pay-per-call API that parses cron expressions, returns the next N fire times, and produces a short English description. Timezone-aware (IANA).

Live: https://cron-explainer.cron-explainer-prod.workers.dev/ Pricing: 0.01 EUR per successful call, prepaid via Stripe Checkout in packs of 500 / 5,000 / 50,000 calls. Non-2xx responses are refunded. No subscription. Keys never expire.

Quick start

1. Get a key at https://cron-explainer.cron-explainer-prod.workers.dev/ (Stripe Checkout, €5 minimum).
2. Copy the key — it's shown exactly once.
3. Call the API:

curl -X POST https://cron-explainer.cron-explainer-prod.workers.dev/v1/explain \
  -H "content-type: application/json" \
  -H "x-api-key: $YOUR_KEY" \
  -d '{"cron":"0 9 * * 1-5","tz":"Europe/Lisbon","n":3}'

Response:

{
  "input": {"cron":"0 9 * * 1-5","tz":"Europe/Lisbon","n":3},
  "valid": true,
  "description": "At 09:00, Monday through Friday",
  "next": ["2026-04-24T08:00:00.000Z","2026-04-27T08:00:00.000Z","2026-04-28T08:00:00.000Z"],
  "flags": {"dst_transition_ahead": false, "ambiguous": false, "notes": []},
  "errors": []
}

Check remaining balance:

curl -H "x-api-key: $YOUR_KEY" \
  https://cron-explainer.cron-explainer-prod.workers.dev/v1/balance

MCP

The server is listed on the official MCP registry as io.github.IdoAzaCalls/cron-explainer with a Streamable HTTP endpoint at POST /mcp. It exposes one tool, explain_cron. Pass your x-api-key as an HTTP header on the MCP transport; billing is identical to the REST path.

Registry entry: https://registry.modelcontextprotocol.io/v0/servers?search=cron-explainer

Endpoints

Method	Path	Purpose
POST	/v1/explain	Parse + describe + next fire times (billed)
GET	/v1/balance	Remaining balance for an x-api-key
POST	/v1/checkout	Create a Stripe Checkout Session
GET	/v1/schema	JSON Schema for request/response
POST	/mcp	MCP Streamable HTTP (JSON-RPC 2.0)
GET	/.well-known/mcp.json	Static tool manifest
GET	/health	Liveness probe
GET	/legal/{tos,privacy,disclaimer,notices}	Legal docs

Limits

• Cron: 5-field POSIX/Vixie syntax (minute, hour, day-of-month, month, day-of-week).
• Timezones: IANA names (e.g. Europe/Lisbon, America/Los_Angeles). Defaults to UTC.
• n clamps to [1, 100].
• Best-effort accuracy. See /legal/disclaimer for warranty terms.
• Zero PII: inputs are cron strings and IANA timezones only. Request and response bodies are never logged.

Stack

TypeScript on Cloudflare Workers. Cron parsing via croner (MIT). English descriptions via cronstrue (MIT). Full NOTICE text at /legal/notices.

Contact

azariaido@gmail.com — billing issues, bug reports, custom pricing.