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Developer Tools — JSON Formatter & Validator, Regex Tester and Cron Explainer

A JSON formatter that validates as you paste and pins errors to a line and column, with pretty-printing, minifying, key sorting, YAML conversion and a tree view. Big integers and key order are kept exactly as written. Other tabs on the same page hold a regex tester for JavaScript regular expressions and a cron explainer that turns an expression into plain English and works out the next run times. Nothing you enter is sent to a server.

JSON Formatter & Validator

Paste JSON and it is checked right away, with any error pinned to its line and column. It pretty-prints, minifies to one line, converts to YAML and shows a tree view — and keeps big numbers and key order exactly as written.

Result
Paste JSON on the left and the result appears here. First time? Try the "Example" button above.
Waiting for input.

Regex Tester

Enter a pattern and flags to color every match in the test string and see capture groups and the replacement result. It runs as-is on your browser's JavaScript regex engine.

Enter a pattern.
Matches

No matches.

$1, $2 insert numbered groups, $<name> a named group and $& the whole match. Leave it empty to skip replacing.

Cron Expression Explainer

Turns a cron expression into a readable sentence and works out the next five run times in the time zone you pick. Standard five-field crontab: minute, hour, day of month, month, day of week.

Field by field
Next run times

    Server cron jobs usually run in the server's time zone. GitHub Actions schedules and many cloud schedulers use UTC, so convert your local time to UTC first (for Korea, subtract nine hours).

    FAQ

    Is the JSON or test text I paste sent to a server?
    No. Checking, converting, matching and calculating all happen inside this browser, and nothing you enter is sent anywhere or stored. It is fine to paste sensitive content such as API responses or config files. Only view settings like the last tab you opened and the indent size are remembered in this browser.
    Does formatting change my numbers or key order?
    No. This formatter reads JSON itself instead of going through JavaScript's JSON.parse, so integers larger than 2^53 (Twitter or Discord IDs, for example) and number spellings like 1.0 stay exactly as written. Numeric keys such as "10" and "2" are not pulled to the front either. If the same key appears twice, both are kept and a warning tells you.
    Does it accept JSON with comments or trailing commas?
    Standard JSON does not allow comments, a comma after the last item or single-quoted strings, so they are shown as errors. Because these are common slips, the message says exactly what is wrong — "A trailing comma is left" or "Single quotes are not allowed" — and where, so you only need to fix that spot.
    Which regex flavor does it use?
    It runs directly on your browser's JavaScript (ECMAScript) regex engine. Named groups, lookbehind and Unicode properties (such as \p{L} with the u flag) are available. Syntax found only in PCRE or Python — possessive quantifiers, atomic groups, \A and \Z — is not supported, so if the pattern is meant for another language, check how its syntax differs.
    What does "Did not finish within 1.5 seconds" mean?
    Patterns with nested quantifiers such as (a+)+$ can backtrack through an explosive number of possibilities on input that does not match, freezing for minutes (catastrophic backtracking). This page runs the regex on a separate worker thread and stops it after 1.5 seconds, so the screen never freezes. If you see this message, the same input could hang a real server too — untangle the nested quantifiers.
    What happens if I set both day of month and day of week?
    In standard crontab, if neither field is an asterisk the job runs when either one matches. For example, 0 9 1 * 1 runs at 9 AM on the 1st of every month and also every Monday. For day of week, 0 and 7 are both Sunday, and English abbreviations like MON and JAN work. The six-field format with seconds (Quartz, Spring) and extensions such as L, W and # are not supported.
    See all questions

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