Before you start: test every pattern with examples that should match and examples that should fail.
Digits only
Anchors plus + require the entire value to contain one or more digits.
Regex: ^\d+$
Optional sign
[+-]? allows one optional plus or minus sign before the digits.
Regex: ^[+-]?\d+$
Simple decimal
An optional non-capturing decimal group can handle basic dot-separated decimals.
Regex: ^[+-]?\d+(?:\.\d+)?$
Convert after validation
Regex checks syntax. Convert the value to a numeric type afterward to apply minimum, maximum, precision, and business rules.
Next step: test it for real
Use the Playground to experiment with the pattern, then practice in the game with feedback on false positives and false negatives.