Encode or Decode Base64 — Free Online Converter

Whether you're a developer inspecting data payloads, troubleshooting access headers, or embedding images in HTML, the base64 encoder decoder gives you instant, client-side conversion between plain text and base64 encoded strings — with zero data leaving your device. Understanding your encoded or decoded output empowers you to debug service responses faster, build more reliable web applications, and handle raw data safely across text-based protocols supporting internet protocols and data transmission.

How to Use This Base64 Encoder/Decoder Tool

This free tool is entirely client-side — everything runs locally in your client environment, so no data is ever submitted to a server. There is no software download required, no sign-up needed, and it is completely ad-free and publicly available. Simply paste your data into the input box and the result appears in the output area instantly.

• To encode base64: Type or paste your plain content into the decoded field and click Encode. Your base64 result will appear immediately in the output section. You can then copy the result with a single click.
• To decode base64: Paste the base64 content into the encoded field and click Decode. The decoded output will display the original plain content or raw representation.
• To decode a file: Upload a raw file (image, PDF, or other raw content) or paste a base64 string representing a file. The tool handles file processing entirely within your client environment — uploaded files are processed locally and nothing leaves the client.

Advanced Options for Raw Data, Character Sets, and Line Breaks

The tool exposes several advanced options that give you precise control over your conversion and interpretation process, particularly when handling raw data or multi-entry inputs:

• Character set selection: Choose your charset from the dropdown — typically UTF-8, but the tool supports many others via an auto-detect option. This character set selection determines how content is converted before conversion or after interpretation. Note that this setting is irrelevant for raw file inputs.
• URL-safe mode (Base64URL): Switch to the web-safe variant when your output strings will appear in addresses, filenames, or access credential strings. This mode is address-safe and filename-safe by design.
• Decode each line separately: Enable this option to interpret each line as an independent data entry — useful when you have multiple data entries separated by line breaks. Prior to processing, all non-encoded whitespace is removed to preserve input integrity.
• Live mode: When enabled, the tool uses your client's built-in script routines to convert instantly, without any server processing or data submission whatsoever. Currently live mode supports only the UTF-8 character set.

All communications with the underlying server infrastructure use secure, protected connections (HTTPS). Any uploaded files are deleted after the first download attempt or after 15 minutes inactivity, whichever comes first. Review the privacy policy for full details on data handling.

Base64 Encoding in Practice: Script Functions, Java, OAuth 2.0, and Access Credentials — A Free Online Tool Reference

Developers encounter base64 encoding across nearly every layer of modern software development — from client-side script routines to back-end services and OAuth 2.0 access flows. This section provides concrete, working code examples and explains the real-world contexts where the conversion operates every day.

Using Base64 in JavaScript with btoa and atob

In scripting environments, the built-in functions btoa() (raw-to-text — the btoa function) and atob() (text-to-raw — the atob function) handle base64 encoding and base64 decoding operations natively in every modern client environment and Node.js runtime. These built-in routines require no external library and enable encode base64 and decode base64 operations with a single line of code.

// JavaScript encoding and decoding with btoa / atob
let text = "Hello, world!";
let encoded = btoa(text);
console.log(encoded); // Outputs: "SGVsbG8sIHdvcmxkIQ=="

let encodedStr = "SGVsbG8sIHdvcmxkIQ==";
let decoded = atob(encodedStr);
console.log(decoded); // Outputs: "Hello, world!"

The console logs above confirm that btoa("Hello, world!") produces the output SGVsbG8sIHdvcmxkIQ==, and atob() reverses it to restore the original content. These JavaScript functions enable smooth data processing, and you can use them to encode binary data for data URIs and inspect payloads during troubleshooting workflows. For non-standard symbols or reserved characters, convert your string to a UTF-8 byte array first to avoid character conversion errors — a common source of issues in web applications.

The btoa/atob pair is ideal for in-browser tasks: converting payloads for network requests, embedding raw content in structured object data, and inspecting payloads received in service responses. You can examine headers, check access headers, and verify the output matches expectations — all without leaving the client environment.

Java Library Support with java.util.Base64

Java 8 introduced native support for the conversion via the java.util.Base64 class, eliminating the need for third-party libraries. The class provides three converters and three interpreters: a basic converter for standard Base64, a web-safe converter, and a content-transfer converter. This library support makes it straightforward to process strings and handle raw data in enterprise applications.

import java.util.Base64;

public class Base64Example {
    public static void main(String[] args) {
        String original = "Hello, world!";

        // Encoding
        Base64.Encoder encoder = Base64.getEncoder();
        String encodedValue = encoder.encodeToString(original.getBytes());
        System.out.println("Encoded: " + encodedValue);
        // Outputs: Encoded: SGVsbG8sIHdvcmxkIQ==

        // Decoding
        Base64.Decoder decoder = Base64.getDecoder();
        byte[] decodedBytes = decoder.decode(encodedValue);
        String decodedText = new String(decodedBytes);
        System.out.println("Decoded: " + decodedText);
        // Outputs: Decoded: Hello, world!
    }
}

The Base64.getEncoder() method returns a Base64.Encoder instance; Base64.getDecoder() returns a Base64.Decoder. For address-safe output in this language, use Base64.getUrlEncoder(), which replaces + with - and / with _ to produce filename-safe output suitable for web addresses. For content-transfer-compatible output with line breaks at 76 characters, use Base64.getMimeEncoder(). Reading a raw asset file and preserving raw data in a database are the most common real-world uses — converting data before storing or transmitting, then restoring it upon retrieval.

Base64 Encoding in OAuth, Signed Credentials, and Web Security

Base64URL is the conversion format at the heart of modern identity and access systems. In OAuth 2.0 and OpenID Connect, JSON Web Tokens (JWT) use base64url to encode each of their three parts: the header, the payload, and the signature. Each section is a base64url-encoded object, separated by dots, forming the compact structure that makes signed credential strings suitable for web headers, addresses, and service responses.

The JWT header typically specifies the algorithm and token type; the payload carries the claims; and the signature is generated by combining the encoded header and payload with a secret or private key using a JSON Web Signature (JWS) algorithm, or by protecting the payload using JSON Web Encryption (JWE). The result is a credential string that is digitally signed (and optionally protected), making it integrity-protected against tampering by unauthorized parties. The message authentication code (MAC) or cryptographic signature means any modification of the base64 content in transit would invalidate the credential — a key guarantee. Signed credential strings are the primary access formats in modern identity systems, carrying claims between client and server.

In the OAuth 2.0 client credentials flow, the client ID and client secret are concatenated with a colon separator (client_id:client_secret) and then base64-encoded. This output is sent in the access header as Authorization: Basic <base64string>, following the web specification for basic identity verification. The server interprets the login details to verify the client's identity. This use of base64 encoding in access headers is one of the most common patterns in protected service communication and credential issuance.

Beyond signed credentials and OAuth, base64 encoding is used throughout web and networking applications for:

• Converting keys and certificates — including public keys, private keys, and protected credentials — in public key cryptography and TLS certificate exchange.
• Embedding raw content (images, PDFs, raw asset data) as inline references inside HTML, structured markup, or CSS — enabling web-friendly text delivery of raw resources and allowing developers to embed assets without separate web requests.
• Converting form data and address parameters that contain raw representations or reserved characters that would otherwise break address format.
• Transmitting access headers and OAuth credential strings across text-based protocols where raw data would cause corruption or loss.
• Converting message attachments via content-transfer standards for messaging, ensuring safe passage through legacy mail systems that are not 8-bit clean.