What is Base64 encoding?

Base64 encodes binary data into ASCII text using 64 printable characters (A-Z, a-z, 0-9, +, /). It's used to embed binary data in text-based formats like JSON, XML, HTML, and email. The encoded output is roughly 33% larger than the input.

How do I encode text to Base64?

Paste your text in the input field and click Encode. The tool converts each character to its UTF-8 bytes and then to Base64 representation. Click Copy to grab the result.

When should I use Base64 encoding?

Common uses include: embedding small images in CSS/HTML (data URIs), sending binary data in JSON APIs, encoding file contents for upload, email attachments (MIME), and storing binary data in text-only databases.

What's the difference between Base64 and Base64URL?

Standard Base64 uses + and / characters, which need escaping in URLs. Base64URL replaces these with - and _ and removes padding (=). JWTs use Base64URL encoding because tokens are often passed in URLs.

Base64 エンコード/デコード

ブラウザで Base64 変換

Input

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Output

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Encode and decode Base64 without trusting an online server

Base64 shows up everywhere — JWT payloads, image data URIs, email attachments, API request bodies. Encoding and decoding it in your browser keeps the data on your machine, which matters when the value is a token, a secret, or anything else you'd rather not paste into a remote service.

Use the tool when you need to

Decode a Base64-encoded value from a header

Inspect Authorization headers, encoded query parameters, or other Base64 strings safely in the browser.

Encode binary data for an API

Convert a small image or file into a Base64 string for inclusion in a JSON request body.

Flip between Base64 and Base64URL

Switch encoding variants when working with JWTs and URL-safe payloads.

How to encode or decode Base64 quickly

1
Paste the input into the text area.
2
Click Encode or Decode based on the direction you need.
3
Copy the result, or download it as a file when working with binary data.

Keep going

Encode URL components

Use percent-encoding when the destination is a URL rather than binary safety.

Decode JWTs

Use the focused decoder when the Base64 value is part of a token.

Format decoded JSON

Beautify the output if the decoded value turns out to be JSON.

Validate decoded JSON

Confirm the decoded JSON parses cleanly before passing it forward.

Common Base64 workflows

Inspect an Authorization header

Decode a Basic auth header to see the raw username and password format being sent.

Embed a small asset in JSON

Encode a tiny image as a data URI and embed it directly in an API request body.

Round-trip token payloads

Decode a JWT segment, edit it, and re-encode it for testing — without server-side help.

よくある質問

Base64は、バイナリデータをASCII文字列に変換するためのエンコード方式です。64種類の印字可能文字（A-Z, a-z, 0-9, +, /）で表現するため、JSON/XML/HTMLやメールのようなテキストベースの形式にバイナリを埋め込む用途でよく使われます。なお、エンコード後のサイズは元データよりおよそ33%増えます。

入力欄にテキストを貼り付けて「Encode」をクリックしてください。このツールは文字列をUTF-8のバイト列に変換したうえでBase64表現にします。結果は「Copy」でコピーできます。

よくある用途は、CSS/HTMLへの小さな画像の埋め込み（data URI）、JSON APIでのバイナリ送信、アップロード用にファイル内容を文字列化するケース、メール添付（MIME）、テキストのみのDBにバイナリを保存するケースなどです。

通常のBase64は + と / を使いますが、これらはURL内ではエスケープが必要になることがあります。Base64URLは + を - に、/ を _ に置き換え、さらにパディング（=）を省略します。JWTはトークンがURLで扱われることが多いため、Base64URLが使われます。