Regex

You might say

AI gave me a regex I cannot read. Should I use it?

A notation describing what text to match, used to find and validate textWhen validating phone numbers, emails, or filtering text in forms, a regular expression uses symbolic patterns to describe what the text should look like, such as \d for digits and + for one or more. You do not have to write complex expressions from scratch, but you should be able to read what they accept and reject, and test them with real examples.

Know first

Validation

Regex

One regex: click inputs and see pass or reject

Validation rule/^\d+$/

Selected: 13800138000 → passes because the whole string is digits

Acceptance must cover rejects: inputs that should be rejected—spaces, letters, empty values—must be confirmed rejected.

Three things to read in a regex

Common symbol meanings: \d is one digit, + is one or more, ^ and $ match the whole string; brackets list allowed characters.

Test it with real inputs: The fastest way to judge a regex is to feed it boundary inputs: pure digits, symbols, and empty values each once.

Acceptance must cover rejects: Testing only passing cases is not acceptance; inputs that should be rejected—spaces, letters, too long—must be confirmed rejected.

Quick checkChoose the best answer

AI uses /^\d+$/ to validate a phone number input. What does it accept?

Any phone number formatAny text at allOnly pure digit strings (one or more); letters, spaces, and +86 do not match

You can say this to an AI Agent

Validate phone numbers with a regex and provide acceptance cases: a pure 11-digit number passes, while spaces, letters, and +86 are rejected. Afterward, run each case and confirm both pass and reject results are correct.

Learn next

1Validation→2Form→3Field→

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