Date Format Reference & Tester
Test date format patterns across 7 languages and copy results instantly.
About This Tool
The Date Format Reference & Tester is a comprehensive, browser-based tool that helps developers quickly look up, compare, and test date formatting patterns across seven popular programming languages and libraries. Whether you are writing a JavaScript application with date-fns, formatting timestamps in Python with strftime, building Java services with DateTimeFormatter, generating PHP date output, working with Go's unique reference-time approach, writing Ruby scripts, or formatting dates in C# with DateTime.ToString, this tool provides the token reference tables and live preview you need.
Every language handles date formatting differently. JavaScript
libraries like date-fns, moment.js, and Day.js use tokens like
yyyy, MM, and dd. Python and Ruby use percent-prefixed
directives like %Y, %m, and %d. Go takes a completely
unique approach by formatting a specific reference time
(Mon Jan 2 15:04:05 MST 2006). PHP's date() function uses
single-letter format characters. This tool lets you switch between
all of them and see live output for your chosen date.
The common format presets section shows your date in ISO 8601, RFC 2822, Unix timestamp, US/EU date formats, 12-hour and 24-hour time, and relative time — all at a glance with one-click copy buttons. The cross-language comparison table displays the same date formatted using each language's default pattern side by side, making it easy to translate format strings when porting code between languages. You can also use the Timestamp Converter for Unix timestamp conversions or the Cron Expression Builder for scheduling expressions that depend on time formats.
All processing happens entirely in your browser. No date values or format strings are sent to any server — your data stays private and the tool works offline after the initial page load.
How to Use
- Select a date and time using the Date / Time picker, or click Now to use the current moment.
- Browse the Common Format Presets table to see your date in ISO 8601, RFC 2822, Unix timestamp, and other popular formats. Click the copy icon next to any row.
- Choose a Library / Language from the dropdown (JavaScript date-fns, Python strftime, Java DateTimeFormatter, PHP date(), Go time.Format, Ruby strftime, or C# DateTime.ToString).
- Enter or modify a Format Pattern in the text field to see the live result update below.
- Review the Token Reference Table for the selected library to understand each token's meaning and its live output for your selected date. Click copy on any token.
- Scroll to the Cross-Language Comparison to see the same date formatted with default patterns across all seven languages.
- Use Ctrl+Shift+C to copy the current formatted result.
Popular Date Format Examples
FAQ
Is my data safe when using this tool?
Yes. All date formatting and pattern processing runs entirely in your browser using JavaScript. No data is transmitted to any server. You can safely use this tool with any date values, including dates from internal systems or private projects.
Which JavaScript libraries are covered?
The JavaScript section covers the token syntax used by date-fns, Day.js, and moment.js, which share very similar format string conventions (yyyy, MM, dd, HH, mm, ss). The tool also shows Intl.DateTimeFormat-style output in the presets section.
Why does Go use a reference time instead of tokens?
Go's time.Format uses a unique approach where you write the reference time 'Mon Jan 2 15:04:05 MST 2006' (which is 01/02 03:04:05 PM '06 -0700) in the format you want. The values 1, 2, 3, 4, 5, 6, 7 in the reference time correspond to month, day, hour, minute, second, year, and timezone. This eliminates the need to memorize abstract tokens.
What is the difference between ISO 8601 and RFC 2822?
ISO 8601 uses the format '2026-02-28T14:30:00Z' with a T separator and Z or offset suffix. RFC 2822 uses the format 'Sat, 28 Feb 2026 14:30:00 +0000' with weekday abbreviation and English month name. ISO 8601 is preferred for APIs and data exchange, while RFC 2822 is used in email headers and HTTP date headers.
Can I test format patterns for dates in different timezones?
The tool formats dates using your browser's local timezone. The timezone offset tokens (like xxx in date-fns, %z in Python, -07:00 in Go, P in PHP) reflect your current local timezone. For timezone conversion between different zones, use the Timestamp Converter or Timezone Converter tool.
What are ordinal dates and day-of-year formats?
Ordinal dates represent the day as a number within the year (1-366). For example, February 28 is day 59 of the year. This format is used in ISO 8601 ordinal date notation (2026-059), Julian dates in aviation and military contexts, and some scientific data formats. Python's %j and PHP's z token produce day-of-year values.
How do week numbering systems differ?
ISO 8601 weeks start on Monday and the first week of the year contains January 4th. US (POSIX) weeks start on Sunday and the first week contains January 1st. This can cause the same date to fall in different week numbers depending on the system. PHP's W token and Python's %V give ISO week numbers.
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