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...

Security Scan

The skill is internally consistent: its name/description match the included Python script and runtime instructions, it requests no credentials or installs, and it performs only local cron-expression parsing and reporting.

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.

Assessment

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.

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