Patterns for common data Updated November 2026

Regex for numbers only

^\d+$ matches a string made only of digits, one or more. \d is the same as [0-9] in JavaScript; in Python 3 and .NET it also matches other Unicode digits unless you write [0-9]. To remove everything that is not a digit, replace \D with an empty string using the g flag.

Syntax

/^\d+$/

Examples

["12345", "12a45", "", "007"].map(s => /^\d+$/.test(s))

Result: [true, false, false, true]

The empty string fails because + needs at least one digit.

"(555) 123-4567".replace(/\D/g, "")

Result: "5551234567"

Keep only the digits.

"Order 66 shipped 12 items".match(/\d+/g)

Result: ["66", "12"]

["-12.50", "3", "1.", ".5"].map(s => /^-?\d+(?:\.\d+)?$/.test(s))

Result: [true, true, false, false]

Optional sign and optional decimal part; digits are required on both sides of the point.

Common mistakes

Using \d* which also matches the empty string; use \d+ when at least one digit is required.
Converting to Number before validating, which turns 007 into 7 and accepts 1e3; test the string first.
Forgetting that \d matches Arabic-Indic and other digits in Python 3; use [0-9] for ASCII only.
Testing without anchors, so abc123 passes because it contains digits.

Practice Regex for numbers only

These drills check your answer on live data, free, no account needed.

Keep only the digitsRemove every character that is not a digit, so phone numbers in any format become plain digits.
One or more: goal, gooal, goooalThe whole line must match. Match g, then one or more o characters, then al. So goal, gooal and goooooal match, but gal does not.
Currency amounts with commasThe whole line must match. Match a dollar amount: $, then 0 or a number without leading zeros that uses a comma every three digits (so $1,234, never $1234), then optionally a period and exactly two digits of cents.

Questions

What is the regex for a number with decimals?

^-?\d+(?:\.\d+)?$ for optional sign and decimals. To also allow .5, use ^-?(?:\d+\.?\d*|\.\d+)$.

How do I allow only numbers in an input field with regex?

Test the value against ^\d*$ on each change (the * allows the field to be empty while typing), or strip non-digits with value.replace(/\D/g, "").

How do I match a number between 1 and 100?

^(?:[1-9]\d?|100)$ : one or two digits not starting with 0, or exactly 100. Ranges in regex are built per digit length.

Regex for letters onlyThe ^[a-zA-Z]+$ pattern for ASCII letters, a Unicode version with \p{L} and the u flag, allowing spaces between words, and stripping non-letters from text.
Regex for alphanumericThe ^[a-zA-Z0-9]+$ pattern, how it differs from \w, how to make a URL slug by replacing everything else, and a Unicode version with \p{L} and \p{N}.
Regex for whitespaceHow \s matches spaces, tabs and newlines, trimming leading and trailing whitespace, collapsing repeated spaces, splitting on whitespace, and detecting blanks.
QuantifiersWhat * + ? {n} {n,} and {n,m} mean, how greedy matching works, how to repeat a group instead of a single character, and the silent {2, 3} mistake.