Regex to Match a Decimal Number
Copy the pattern, paste your text below, and see every decimal it matches. Below the tester: how it handles signs, leading dots, and integers.
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What this pattern matches
This matches decimal numbers with an optional sign, whether written as 3.14, 42, or .75.
How it works, part by part
[-+]? — an optional leading sign.
\d+\.?\d* — digits with an optional decimal point and more digits (covers 42 and 3.14).
|\.\d+ — or a leading-dot form like .75.
Strict validation
To validate a whole field as one number, anchor it with ^…$. As written it will find each number inside 1.2.3 separately rather than rejecting it.
Use it in your code
Python
import re
text = "Valid: 3.14, -0.5, +42, .75, 100. Not matched cleanly: 1.2.3 (two numbers)."
pattern = r'''[-+]?(?:\d+\.?\d*|\.\d+)'''
for m in re.finditer(pattern, text):
print(m.group())JavaScript
const text = "Valid: 3.14, -0.5, +42, .75, 100. Not matched cleanly: 1.2.3 (two numbers).";
const re = new RegExp(String.raw`[-+]?(?:\d+\.?\d*|\.\d+)`, "g");
console.log(text.match(re));FAQ
Does it match leading-dot numbers like .5?
Yes. The second alternative \.\d+ handles .5 and .75.
Does it accept a plus sign?
Yes. The optional [-+] leading sign matches both +42 and -0.5.
How do I reject 1.2.3?
Anchor the pattern with ^ and $ so the whole input must be a single valid number.