What do %s, %d, and %f do?

%s inserts an argument as-is (as text), %d inserts it as a truncated integer, and %f inserts it as a plain number. %% inserts a literal percent sign and doesn't consume an argument.

What happens if I don't supply enough arguments?

The tool reports an error naming how many arguments were provided, rather than silently leaving a placeholder unfilled.

Are arguments matched by position or by name?

By position: the first placeholder consumes the first argument line, the second placeholder consumes the second, and so on, matching classic printf() behavior.

Printf Tool Online - %s %d %f Substitution

Overview

Introduction

The printf format-string convention, %s for strings, %d for integers, %f for floats, is familiar from C and many other languages.

This tool applies that same substitution to arbitrary text.

What Is Printf Tool?

A printf-style formatter that scans a format string for %s, %d, %f, and %% placeholders and fills them in from a list of arguments, one per line, in order.

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 Printf Tool Works

The tool matches each placeholder in the format string with a regex, consuming one argument per placeholder in order (except %%, which needs none) and formatting it according to the placeholder type.

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

When To Use Printf Tool

Use it to preview what a printf() call would output, or to quickly assemble formatted text from a template and a list of values.

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 Find & Replace Tool and Text Joiner.

Features

Advantages

Supports the three most common printf conversions plus the literal %% escape.
Reports a clear error when arguments run out instead of silently leaving gaps.

Limitations

Doesn't support printf's full width/precision/flag syntax (like %05d or %.2f), only the bare conversion characters.

Examples

Filling in a greeting template

Input

Hello, %s! You are %d years old.

Output

Hello, Ada! You are 36 years old.

With arguments 'Ada' and '36', the %s and %d placeholders are filled in order.

Best Practices & Notes

Best Practices

List arguments in the exact order their placeholders appear in the format string.

Developer Notes

Placeholder matching uses a single regex (`/%[sdif%]/g`) with a replacer function that tracks an argument index closure, consuming one argument per non-%% match; a `missing` flag set inside the replacer signals an error after the replace pass completes.

Printf Tool Use Cases

Previewing printf() output before writing the equivalent code
Assembling formatted text from a template and a list of values
Teaching or demonstrating printf-style substitution

Common Mistakes

Expecting width/precision modifiers like %05d to work; only bare conversions are supported.
Providing arguments in the wrong order relative to their placeholders.

Tips

Use %% wherever you need a literal percent sign in the output.

Printf Tool