ISO 8601 DateTime Validation Regex

Validate dates and times in ISO 8601 format with optional timezone, milliseconds, and time components using regex.

Pattern Breakdown

^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:Z|[+-]\d{2}:\d{2})?$

Components

Detailed Breakdown

• \d{4}-\d{2}-\d{2} - Date part: YYYY-MM-DD
• T - ISO 8601 date/time separator (literal T)
• \d{2}:\d{2}:\d{2} - Time part: HH:MM:SS
• (?:\.\d+)? - Optional milliseconds:
  • (?:...) - Non-capturing group
  • \. - Literal dot
  • \d+ - One or more digits
  • ? - Makes entire group optional
• (?:Z|[+-]\d{2}:\d{2})? - Optional timezone:
  • Z - UTC timezone indicator
  • \| - OR operator
  • [+-] - Plus or minus sign
  • \d{2}:\d{2} - Timezone offset HH:MM
  • ? - Makes entire group optional

Examples

Valid:

• 2024-03-15T12:30:45
• 2024-03-15T12:30:45Z (UTC)
• 2024-03-15T12:30:45+05:30 (IST)
• 2024-03-15T12:30:45-08:00 (PST)
• 2024-03-15T12:30:45.123Z (with milliseconds)
• 2024-03-15T12:30:45.123456789+05:30 (with nanoseconds)
• 2024-03-15T00:00:00Z (midnight UTC)

Invalid:

• 2024-3-15T12:30:45 (month not zero-padded)
• 2024-03-15 12:30:45 (space instead of T)
• 2024-03-15T12:30:45+5:30 (timezone offset not zero-padded)
• 2024-03-15T25:00:00 (invalid hour)
• 2024-13-15T12:30:45 (invalid month)
• 24-03-15T12:30:45 (year too short)

Implementation

JavaScript

const iso8601Regex = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:Z|[+-]\d{2}:\d{2})?$/;
iso8601Regex.test('2024-03-15T12:30:45Z'); // true
iso8601Regex.test('2024-03-15T12:30:45+05:30'); // true
iso8601Regex.test('2024-03-15T12:30:45.123Z'); // true
iso8601Regex.test('2024-03-15T25:00:00'); // false (invalid hour)

Python

import re
iso8601_regex = r'^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:Z|[+-]\d{2}:\d{2})?$'
bool(re.match(iso8601_regex, '2024-03-15T12:30:45Z'))  # True
bool(re.match(iso8601_regex, '2024-03-15T12:30:45+05:30'))  # True
bool(re.match(iso8601_regex, '2024-03-15T25:00:00'))  # False (invalid hour)

Go

iso8601Regex := regexp.MustCompile(`^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:Z|[+-]\d{2}:\d{2})?$`)
iso8601Regex.MatchString("2024-03-15T12:30:45Z") // true
iso8601Regex.MatchString("2024-03-15T12:30:45+05:30") // true
iso8601Regex.MatchString("2024-03-15T25:00:00") // false (invalid hour)

Limitations

1. No date/time validation: Accepts invalid dates like 2024-02-30T12:00:00
2. No hour/minute validation: Accepts 2024-03-15T25:00:00 (format valid, time invalid)
3. No timezone validation: Doesn't verify if timezone offset is valid
4. Format only: Validates format, not actual datetime validity
5. No week dates: Doesn't support ISO 8601 week dates (YYYY-Www-D)

When to Use

• ISO 8601 datetime format validation
• API datetime parameters
• Database datetime field validation
• International datetime standards
• When you need timezone-aware datetimes
• Logging and timestamp formats

For production, consider:

• Additional validation for actual date/time validity
• Using datetime parsing libraries (e.g., Date.parse() in JS, datetime in Python)
• Validating timezone offsets
• Handling edge cases (leap seconds, etc.)
• Combining with datetime object validation