Find & Replace

Q: Can the replacement box use $1 in regex mode?

Yes. The replacement supports backreferences like $1 $2 referencing capture groups in the regex.

Q: How do ignore-case and regex work together?

When both "Regex" and "Ignore case" are checked, the i flag is added automatically so matching is case-insensitive.

Support plain text and regex, optional case-insensitive, replace everywhere

Original text

Result

Find Replace with

Regex Ignore case

Find and replace: the difference between plain text and regex mode

The essential difference between the two modes

	Plain mode	Regex mode
Find field	Literal substring	Pattern (metacharacters carry special meaning)
Special characters	All ordinary, no escaping needed	`. * + ? ( ) [ ] { } \| ^ $ \` must be escaped
Replace field	Written verbatim	`$1`, `$&` and similar reference capture groups
Typical use	Rename a token, swap a separator, delete a word	Reformat, normalize by pattern, extract and reorder

For "replace a word", plain mode is the safest choice — you do not think about any escaping at all. Switch to regex mode and a . suddenly means "any character", a ( becomes the start of a group, and an unpaired bracket throws an error on the spot.

Replacement references in regex mode

This is where regex replacement earns its keep — it does not merely substitute, it restructures:

Replacement syntax	Meaning
`$1` `$2`	Contents of the first, second capture group
`$&`	The entire matched text
`$` followed by a backtick	Text before the match (that character cannot be written directly here; see MDN on String.replace)
`$'`	Text after the match
`$$`	A literal dollar sign

Practical example — turn 2026-01-15 into 15/01/2026: find (\d{4})-(\d{2})-(\d{2}), replace with $3/$2/$1. Plain mode cannot do this, because it is a "reorder", not a "replace".

Another one: indent the start of every line. Find ^(\S), replace with $1 (with the multiline flag on).

Three places that bite

In plain mode $ is a literal, but in a regex replacement it is a reference prefix. To emit a literal dollar sign, write $ in plain mode; in regex mode write $$.
Ambiguity in backreference numbers. $12 is read as the twelfth capture group (if it exists), not "group 1 followed by the character 2". When you need the latter, write $1 then 2 separately, without a space, or use a named group.
The ignore-case flag affects find only, never replace. The replacement text is written exactly as you give it; its casing is your decision. To turn both color and Color into colour, tick ignore-case; but to preserve each original casing you need two replacement passes or a $&-based trick.

Check before you act

Batch replace is irreversible unless you kept the original. Suggested flow:

First confirm the pattern matches what you intend with the regex tester — look at match count and each matched span.
Watch for accidental matches. Replacing id will hit userId, valid, hidden — use a word boundary \bid\b to avoid that.
Read through the result after replacing; do not just trust "replacement done".
Keep a copy of the source. The output is read-only, and the original still sits in the input box, but if you keep editing inside the input box you overwrite it.

Replacement runs locally in your browser; text containing sensitive information is never uploaded.

FAQ

Can the replacement box use $1 in regex mode?

Yes. The replacement supports backreferences like $1 $2 referencing capture groups in the regex.

How do ignore-case and regex work together?

When both "Regex" and "Ignore case" are checked, the i flag is added automatically so matching is case-insensitive.