Base64
エンコードと暗号化 · 無料オンラインツール
UTF-8 対応の Base64 エンコードとデコード。
Click "Encode" or "Decode" to transform your text...エンコード
Unicode や emoji を含む任意のテキストを Base64 文字列に変換し、安全に転送。
デコード
Base64 文字列を貼り付けて元の UTF-8 テキストを即座に復元。明確なエラーフィードバック付き。
UTF-8 セーフ
TextEncoder による完全な UTF-8 サポート——CJK 文字、emoji、記号を正しく処理。
Base64の使い方
- 1Enter or paste your data into the input field.
- 2Select the desired encoding, hashing, or encryption options.
- 3Click the action button to process your data.
- 4Copy the result from the output field.
機能と特徴
- ✓完全無料 — 登録不要、サブスクリプションなし、広告なし
- ✓ブラウザ上で完全に動作 — データは端末から送信されません
- ✓高速・軽量 — 即座に結果を表示
- ✓クロスプラットフォーム — デスクトップ・タブレット・モバイル対応
Base64とは？
Base64 is a binary-to-text encoding scheme defined by RFC 4648 that converts binary data into a set of 64 ASCII characters (A-Z, a-z, 0-9, +, /). It is NOT encryption — it is fully reversible and requires no key. Base64 is commonly used for MIME email, Data URLs, JWT payloads, and embedding binary resources in JSON/XML.
Base64の仕組み
Base64 processes input data in 3-byte (24-bit) blocks, splitting each block into four 6-bit groups. Each 6-bit value maps to one of 64 characters. If the input length is not divisible by 3, padding (=) is appended. UTF-8 text is first encoded to bytes before Base64 encoding.
よくある使用例
- ✓API token encoding — pass binary tokens safely in HTTP headers
- ✓Email attachments — MIME encodes binary files as Base64 for text-based transport
- ✓Data URLs — embed small images directly in HTML/CSS as Base64 strings
- ✓JWT tokens — the header and payload sections use Base64URL encoding
Base64 vs Encryption
Base64 is encoding; encryption is a different operation. Base64 is reversible by anyone (no key needed) — its purpose is format compatibility, not confidentiality. Encryption (AES, RSA) requires a key and is designed to hide data. Use Base64 when you need to transport binary data through text-only channels; use encryption when you need to protect data from being read.
セキュリティとプライバシー
This tool runs entirely in your browser — your data is never uploaded to any server. Base64 itself provides NO security; never use it to protect sensitive data. For password storage use Bcrypt; for confidentiality use AES encryption.
技術的な詳細
Standard: RFC 4648. Character set: A-Z, a-z, 0-9, +, / (URL-safe variant uses - and _). Padding: one or two = characters. A 1MB input produces ~1.33MB Base64 output (33% size increase). Base64URL (used in JWT) replaces +/ with -_ and omits padding.
よくある質問
Is Base64 encryption?
No. Base64 is encoding, not encryption. Anyone can decode it without a key. It converts binary to text for transport compatibility, not for security.
Why does Base64 make data larger?
Base64 encodes every 3 bytes into 4 characters, causing a ~33% size increase. This overhead is the trade-off for text-only compatibility.
What is Base64URL?
Base64URL is a URL-safe variant (RFC 4648 §5) that replaces + with - and / with _, and omits padding. It is used in JWT tokens and URL parameters.
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