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Crontab Validator
by
charlie-morrison
· GitHub ↗
· v1.0.0
· MIT-0
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Install in OpenClaw
/install crontab-validator
Description
Validate, explain, lint, and calculate next run times for cron expressions. Use when asked to check cron syntax, explain a crontab entry, find next scheduled...
README (SKILL.md)
Crontab Validator & Explainer
Validate cron syntax, get human-readable explanations, calculate next run times, and lint for common mistakes.
Validate
# Single expression
python3 scripts/cron_check.py validate "*/15 * * * *"
# Multiple expressions with lint
python3 scripts/cron_check.py validate --lint "0 2 * * *" "* * * * *" "0 0 31 2 *"
Explain in Detail
python3 scripts/cron_check.py explain "30 4 1,15 * 1-5"
Next Run Times
# Next 5 runs (default)
python3 scripts/cron_check.py next "0 9 * * 1-5"
# Next 10 runs
python3 scripts/cron_check.py next "0 */6 * * *" --count 10
# From specific time
python3 scripts/cron_check.py next "0 9 * * *" --from-time 2026-01-01T00:00:00
Lint
# Check for common mistakes
python3 scripts/cron_check.py lint "* * * * *" "0 0 31 2 *" "0 0 29 2 *"
# Strict mode (exit 1 on warnings)
python3 scripts/cron_check.py lint --strict "0 0 31 4 *"
Output Formats
python3 scripts/cron_check.py -f json explain "0 9 * * 1-5"
python3 scripts/cron_check.py -f markdown validate --lint "*/5 * * * *"
Supported Syntax
| Feature | Example | Description |
|---|---|---|
| Wildcard | * |
Every value |
| Specific | 5 |
Exact value |
| Range | 1-5 |
Values 1 through 5 |
| List | 1,3,5 |
Values 1, 3, and 5 |
| Step | */15 |
Every 15th value |
| Range+Step | 1-30/2 |
Odd values 1-30 |
| Names | mon-fri |
Day/month names |
| Shortcuts | @daily |
Predefined schedules |
Shortcuts
| Shortcut | Equivalent | Meaning |
|---|---|---|
@yearly |
0 0 1 1 * |
Once a year |
@monthly |
0 0 1 * * |
First of month |
@weekly |
0 0 * * 0 |
Every Sunday |
@daily |
0 0 * * * |
Every midnight |
@hourly |
0 * * * * |
Every hour |
Lint Checks
| Check | Level | Description |
|---|---|---|
| Every-minute | Warning | * * * * * runs 1440 times/day |
| Day 31 in short months | Warning | Apr, Jun, Sep, Nov have 30 days |
| Feb 29-31 | Warning | Only runs in leap years (29) or never |
| DOM + DOW conflict | Info | Both specified = OR logic |
| High frequency | Info | More than 288 runs/day |
Usage Guidance
This skill is a local Python-based cron-expression linter/explainer and appears coherent with its description. Before installing: ensure you trust the source (it will execute a local Python script), run it in a limited environment if you have concerns, and verify you have python3 available. Note that I observed minor logic/weekday handling quirks in the code (which can affect correctness of some edge cases) but no signs of data exfiltration, network calls, or secret access. If you need absolute correctness for production schedules, consider reviewing or testing the script against known cron examples first.
Capability Analysis
Type: OpenClaw Skill
Name: crontab-validator
Version: 1.0.0
The crontab-validator skill is a well-implemented utility for parsing, explaining, and linting cron expressions. The core logic in scripts/cron_check.py uses standard Python libraries (re, datetime, argparse) to process inputs and contains no risky execution patterns, network activity, or file system access. The SKILL.md instructions are strictly limited to the tool's stated functionality and do not exhibit any signs of prompt injection or malicious intent.
Capability Assessment
Purpose & Capability
The advertised functionality (validate, explain, lint, and compute next runs for cron expressions) is implemented by scripts/cron_check.py and the SKILL.md usage examples map directly to the script's CLI. No unrelated capabilities (cloud access, system administration, or network calls) are requested or present.
Instruction Scope
SKILL.md instructs the agent to run the included python script with explicit arguments. The instructions do not reference reading unrelated files, environment variables, or external endpoints. The script's imports are limited to standard Python libraries and it performs only local computation. Note: the implementation contains non-security correctness quirks in weekday handling (minor logic inconsistencies), but these are functional bugs rather than scope creep.
Install Mechanism
No install spec is provided; the skill is instruction+script only and expects a python3 runtime to be present. Nothing is downloaded or written during install.
Credentials
The skill requires no environment variables, credentials, or config paths. There are no requests for secrets or unrelated service tokens.
Persistence & Privilege
The skill is not marked always:true and does not request permanent presence or modify other skills or system-wide settings. It runs on demand as a local Python script.
How to Use
- Make sure OpenClaw is installed (local or Docker)
- Run the install command in chat:
/install crontab-validator - After installation, invoke the skill by name or use
/crontab-validator - Provide required inputs per the skill's parameter spec and get structured output
Version History
v1.0.0
Initial release
Metadata
Frequently Asked Questions
What is Crontab Validator?
Validate, explain, lint, and calculate next run times for cron expressions. Use when asked to check cron syntax, explain a crontab entry, find next scheduled... It is an AI Agent Skill for Claude Code / OpenClaw, with 94 downloads so far.
How do I install Crontab Validator?
Run "/install crontab-validator" in the OpenClaw or Claude Code chat to install it in one step — no extra setup required.
Is Crontab Validator free?
Yes, Crontab Validator is completely free, licensed under MIT-0. You can download, install and use it at no cost.
Which platforms does Crontab Validator support?
Crontab Validator is cross-platform and runs anywhere OpenClaw / Claude Code is available (cross-platform).
Who created Crontab Validator?
It is built and maintained by charlie-morrison (@charlie-morrison); the current version is v1.0.0.
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