Regex Generator

Input

What should the pattern match?

Email addresses on the company domains acme.com and acme.co.uk, case-insensitive. Reject everything else, including gmail and addresses with nothing before the @.

Regex flavor

JavaScript / TypeScript

Examples that must match (one per line)

[email protected] [email protected]

Examples that must not match (one per line)

[email protected] @acme.com

Strictness

Practical (readable, covers common cases)

Output (excerpt)

```javascript
/^[a-z0-9._%+-]+@acme\.(?:com|co\.uk)$/i
```

**Flags:** `i` — domains and local parts are compared case-insensitively.

| Token | Meaning |
|---|---|
| `^` … `$` | the whole string must be the address |
| `[a-z0-9._%+-]+` | local part: one or more letters, digits or the common punctuation |
| `@acme\.` | literal @acme. — the dot is escaped |
| `(?:com\|co\.uk)` | exactly one of the two company domains |

| Input | Expected | Why |
|---|---|---|
| `[email protected]` | match | plain local part, allowed domain |
| `[email protected]` | match | dot in local part, second domain |
| `[email protected]` | no match | domain not in the list |
| `@acme.com` | no match | empty local part |
| `[email protected]` | no match | anchored, nothing may follow |…

Input

What should the pattern match?

ISO calendar dates like 2026-09-20 anywhere inside a line of text. Month 01-12, day 01-31. Do not match 2026-13-01 or 26-09-20.

Regex flavor

Python (re)

Examples that must match (one per line)

deployed 2026-09-20 at 05:01 2024-02-29

Examples that must not match (one per line)

2026-13-01 26-09-20

Strictness

Strict (rejects everything invalid)

Output (excerpt)

```python
r"(?<!\d)(\d{4})-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])(?!\d)"
```

**Flags:** none. The pattern is not anchored because the date sits inside a line.

| Token | Meaning |
|---|---|
| `(?<!\d)` | not preceded by a digit — rejects `12026-09-20` |
| `(\d{4})` | four-digit year, captured |
| `(0[1-9]\|1[0-2])` | month 01-12 |
| `(0[1-9]\|[12]\d\|3[01])` | day 01-31 |
| `(?!\d)` | not followed by a digit |

**Edge cases:** the pattern does not know month lengths — `2026-02-31` matches. Validate with `datetime.date.fromisoformat()` after extracting, which the usage snippet shows…