What does \d mean in regex?
The digit class, and what it does and does not include.
/^\d{3}-\d{2}-\d{4}$/
Match a whole string consisting of exactly 3 of a digit, then "-", then exactly 2 of a digit, then "-", then exactly 4 of a digit.
What to check
Note
Anchors match string ends, not line ends
Without the m flag, ^ and $ match only the very start and end of the input — not the start and end of each line. On multi-line input this is often not what was intended.
Fix: Add the m flag if the pattern should apply per line.
Step by step
^Anchor to the start of the input.
\d{3}Match exactly 3 of a digit.
-Match "-".
\d{2}Match exactly 2 of a digit.
-Match "-".
\d{4}Match exactly 4 of a digit.
$Anchor to the end of the input.
Details
- Capture groups
- None
- Flags
- None set
Check your own pattern
Paste one on the home page, or call the API or MCP server. This page is also available as markdown.