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CronSpell

by cronspell.mike-tusa.workers.dev · remote · no sign-in to list tools · v0.1.0 · published by dev.workers.mike-tusa.cronspell

Validate and explain cron expressions; list next/previous run times in any time zone, DST-aware.

Changes · 2
CompareRegistry entry

4 tools: 2 change things and 2 only read.

Scanned Oct 22, 2026

2 checks matched something in the tool definitions. No finding is not a safety guarantee. How the checks work.

claude mcp add --transport http cronspell https://cronspell.mike-tusa.workers.dev/mcp

Findings

Matches of fixed checks, with the text they matched.

2 warn
  • Warnnext_cron_runs

    The server marks "next_cron_runs" read-only (readOnlyHint: true), and its own name, description or input give the class "write".

    Matched text

    annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "next_cron_runs" says "run": a word for a change.

    What this check looks for
  • Warncron_runs_between

    The server marks "cron_runs_between" read-only (readOnlyHint: true), and its own name, description or input give the class "write".

    Matched text

    annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "cron_runs_between" says "run": a word for a change.

    What this check looks for

Tools

Open a tool for its reasons and full description. Descriptions are the publisher's own words, shown as they are.

4 tools

Changes things 2Claude Code: ask
  • cron_runs_betweenList every run of a cron expression between start and end (both inclusive) in an IANA time zone, DST-aware, oldest first.1 finding

    Why it is in this group

    • The name "cron_runs_between" says "run": a word for a change.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.

    Findings

    • Warn

      The server marks "cron_runs_between" read-only (readOnlyHint: true), and its own name, description or input give the class "write".

      Matched text

      annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "cron_runs_between" says "run": a word for a change.

      What this check looks for
    Description, as the server wrote it
    List every run of a cron expression between start and end (both inclusive) in an IANA time zone, DST-aware, oldest first. Default limit 20, max 100; truncated is true when there are more. Read-only. Same engine as GET /api/between.

    Annotations the server declares

    • title: List cron runs in a window
    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false
  • next_cron_runsList the next (or, with direction "previous", the most recent past) run times of a cron expression in an IANA time zone, DST-aware.1 finding

    Why it is in this group

    • The name "next_cron_runs" says "run": a word for a change.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.

    Findings

    • Warn

      The server marks "next_cron_runs" read-only (readOnlyHint: true), and its own name, description or input give the class "write".

      Matched text

      annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "next_cron_runs" says "run": a word for a change.

      What this check looks for
    Description, as the server wrote it
    List the next (or, with direction "previous", the most recent past) run times of a cron expression in an IANA time zone, DST-aware. Each run has the local time with its UTC offset, the UTC time, unix seconds and weekday. Default 5 runs, max 20; searches up to 50 years. Read-only. Same engine as GET /api/next and GET /api/previous.

    Annotations the server declares

    • title: List cron run times
    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false
Only reads 2Claude Code: allow
  • explain_cronExplain a cron expression in plain English, e.g.No findings

    Why it is in this group

    • The name "explain_cron" says "explain": a word for reading.
    Description, as the server wrote it
    Explain a cron expression in plain English, e.g. "0 9 * * 1-5" → "At 09:00, on Monday through Friday." Also returns notes on cron rules that often surprise people (day-of-month OR day-of-week, seconds field, shorthand expansion). Invalid expressions return isError with the reason. Read-only. Same engine as GET /api/explain.

    Annotations the server declares

    • title: Explain a cron expression
    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false
  • validate_cronCheck whether a cron expression is valid.No findings

    Why it is in this group

    • The name "validate_cron" says "validate": a word for reading.
    Description, as the server wrote it
    Check whether a cron expression is valid. Returns valid true with the expanded values of every field (minute, hour, day of month, month, day of week, and seconds for 6-field expressions), or valid false with an error code, the field at fault and a message. Detects schedules that can never run (e.g. February 30). Read-only. Same engine as GET /api/validate.

    Annotations the server declares

    • title: Validate a cron expression
    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Install

Pinned to version 0.1.0. Values in angle brackets are yours to fill in.

claude mcp add --transport http cronspell https://cronspell.mike-tusa.workers.dev/mcp

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json
{
  "permissions": {
    "allow": [
      "mcp__cronspell__validate_cron",
      "mcp__cronspell__explain_cron"
    ],
    "ask": [
      "mcp__cronspell__next_cron_runs",
      "mcp__cronspell__cron_runs_between"
    ],
    "deny": []
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. It assumes the server is installed as cronspell. Review it before you use it.