Question 1

What does the ISO 8601 Date regex pattern do?

Accepted Answer

Matches 4-digit year, followed by month (01-12) and day (01-31) separated by hyphens. Does not validate month-day combinations (e.g., Feb 31 passes).

Question 2

How do I use the ISO 8601 Date regex in JavaScript?

Accepted Answer

Use the pattern /\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])/g with the String.match() or String.matchAll() method. For example: const matches = text.match(/\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])/g);

Question 3

What regex flags does this pattern use?

Accepted Answer

This pattern uses the global flag (g). The global flag finds all matches in the input, not just the first.

Question 4

Which programming languages support this regex?

Accepted Answer

Fully supported in JS, PYTHON, JAVA, PHP, GO, RUBY, CSHARP

Question 5

What strings does this regex match?

Accepted Answer

This pattern matches strings like: 2024-01-15, 2023-12-31, 1999-06-30. It does not match strings like: 2024-13-01, 2024-00-15, 24-01-15.

Question 6

When should I use the ISO 8601 Date regex?

Accepted Answer

Use this pattern to extract or quick-validate dates in YYYY-MM-DD format from log files, CSV data, API responses, or form inputs. ISO 8601 is the international standard used in databases, REST APIs, and data interchange. Note: this pattern validates format and basic range only — it does not check calendar correctness (e.g., 2024-02-30 passes). Always parse with a date library after regex matching for full validation.

Question 7

What are common mistakes with the ISO 8601 Date regex?

Accepted Answer

A common mistake is: Using \d{2} for the month instead of (?:0[1-9]|1[0-2]). Instead, use (?:0[1-9]|1[0-2]) because \d{2} accepts invalid months like 00 and 13. The alternation constrains months to the valid 01-12 range.. A common mistake is: Assuming the regex validates real calendar dates. Instead, use Use Date.parse() or datetime.strptime() after matching because This pattern cannot detect impossible dates like February 30 or April 31. Regex checks format; a date library checks calendar validity.. A common mistake is: Not anchoring the pattern when validating a full string. Instead, use ^\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])$ because Without ^ and $ anchors, the pattern matches substrings — e.g., it finds '2345-01-01' inside '12345-01-01'. Add anchors when the entire input must be a date.

Question 8

How does the ISO 8601 Date regex work step by step?

Accepted Answer

`\d{4}` — Match exactly 4 digits — the year (e.g., 2024). `-` — Match a literal hyphen separating year from month. `(?:0[1-9]|1[0-2])` — Match month 01-12: either 0 followed by 1-9, or 1 followed by 0-2. `-` — Match a literal hyphen separating month from day. `(?:0[1-9]|[12]\d|3[01])` — Match day 01-31: 01-09, 10-29, or 30-31

Token	Explanation
`\d{4}`	Match exactly 4 digits — the year (e.g., 2024)
`-`	Match a literal hyphen separating year from month
`(?:0[1-9]\|1[0-2])`	Match month 01-12: either 0 followed by 1-9, or 1 followed by 0-2
`-`	Match a literal hyphen separating month from day
`(?:0[1-9]\|[12]\d\|3[01])`	Match day 01-31: 01-09, 10-29, or 30-31

Language	Support
JS	Full support
PYTHON	Full support
JAVA	Full support
PHP	Full support
GO	Full support
RUBY	Full support
CSHARP	Full support

ISO 8601 Date

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Step-by-Step Breakdown

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With slashes

Related Patterns

US Date Format (MM/DD/YYYY)

ISO 8601 DateTime

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