Does it add the prefix to every line, or just once?

The prefix is added once, to the very front of the whole input, not to each line. If you need per-line prefixing, use Find and Replace with an empty find pattern isn't quite right; consider processing lines individually instead.

Does it add the prefix to every line?

No, only once, at the very start of the text. Use the Line Prefix Adder when every line needs to receive the prefix instead.

Is a separator inserted between the prefix and the text?

No. The two are concatenated exactly as given, so include any space, slash, or punctuation you want as part of the prefix itself.

String Prefix Adder Online - Prepend Text to a String

Overview

Introduction

Adding a fixed prefix to text, a namespace, a protocol, a tag, is a one-line operation in code but still convenient to have as a standalone tool for quick edits.

It runs entirely client-side, so nothing you paste is ever uploaded to a server.

What Is String Prefix Adder?

A prefixing tool that concatenates your chosen prefix in front of the input text.

It runs entirely client-side as part of this site's String Tools collection, so nothing you paste is ever uploaded to a server.

How String Prefix Adder Works

The tool simply returns `prefix + input`.

The transformation happens synchronously in JavaScript the moment you type, with no network round trip involved.

When To Use String Prefix Adder

Use it to quickly prepend a namespace to an identifier, a protocol to a URL, or a tag to a filename.

It's a fast way to get the answer without opening a code editor, a REPL, or writing a one-off script just to check.

Often used alongside String Suffix Adder and Find & Replace Tool.

Features

Advantages

Simple and predictable, a direct string concatenation.
Concatenates without trimming either side, so leading whitespace in your text is preserved precisely where it was.
Treats the whole input as one value, which is what makes it safe for multi-line text that needs to keep its structure.

Limitations

Adds the prefix once to the whole input, not per line.
Adds the prefix a single time, so prefixing a list of values means running it once per value.

Examples

Prepending a namespace

Input

world

Output

Hello, world

With prefix 'Hello, ', the result is the prefix followed directly by the input.

Best Practices & Notes

Best Practices

For per-line prefixing across multiple lines, process each line individually rather than relying on a single whole-input prefix.
Include the separator in the prefix itself, such as a trailing slash for a path or a colon for a namespace.
Check for a doubled separator when the text already begins with one, since nothing is deduplicated for you.

Developer Notes

The implementation is a single string concatenation (`prefix + input`), with no per-line splitting.

String Prefix Adder Use Cases

Prepending a namespace to a variable or identifier
Adding a protocol prefix to a bare domain
Tagging a filename with a fixed prefix

Common Mistakes

Expecting the prefix to be added to every line of multi-line input.
Expecting per-line behaviour and pasting in a whole list, which then receives the prefix only on its first line.

Tips

Use Add a Suffix to a String for the equivalent operation at the end of the text.
Pair it with the String Suffix Adder to wrap a value on both sides, such as building a complete URL from a path fragment.

String Prefix Adder