Code 4
Regex, SQL formatting, cron parsing and diff
Expressions that are easy to write and hard to read: cron schedules, regular expressions, SQL that arrived as a single line. These tools turn them back into something you can check.
// Tools in this category
Regex Tester
Test a regular expression against your text and see every match highlighted in place, with capture groups and positions listed. Runs in your browser.
SQL Formatter
Turn a single-line SQL query into indented, readable SQL with keywords aligned. Handles SELECT, JOIN, WHERE, GROUP BY and subqueries, in your browser.
Cron Expression Parser
Decode any cron expression into plain English and list the next 5, 10 or 20 run times. Presets, field guide and validation. Runs entirely in your browser.
Diff Checker
Compare two pieces of text and see exactly what was added, removed and left alone, by line or by character. Runs in your browser with nothing uploaded.
// The cost of a misread expression
A cron field that you read as "every five minutes" but that actually means "at five past every hour" will not fail loudly. It will quietly run 12 times less often than you expected, and you may not notice for weeks. The same is true of a regex that looks right and silently fails on one input class. Checking the expression against a tool that expands it into concrete run times or concrete matches is usually faster than reasoning it through.
// Watch the time zone
Cron run times are computed in the time zone of the machine you are on. The host that actually runs the job has its own, and containers and cloud runners default to UTC, so 09:00 in a crontab on a UTC host is not 09:00 for a team in Tokyo or Berlin. When a schedule matters to people rather than to machines, translate it with the Time Zone Converter before you commit it.
// What to reach for
The Cron Expression Parser accepts standard five-field expressions, explains each field in plain English and lists the next run times. The Regex Tester highlights matches in place and lists capture groups. The SQL Formatter turns a logged one-liner back into something readable. The Diff Checker compares two texts by line or by character.
// Code: frequently asked questions
- Which cron dialect is supported?
- The standard five-field format used by Linux crontab. Extensions such as the seconds field used by Quartz and the @reboot style shorthands are not expanded.
- Do the predicted run times account for daylight saving?
- Run times are computed in your browser local time zone, so they follow that zone daylight saving rules. If the job runs on a UTC host, read the times as a pattern rather than as wall-clock times for your users.
// Other categories
Looking for something that is not here yet? The Japanese edition of this category lists 4 tools. The tools themselves work the same way regardless of the language of the surrounding page.