Base64 Encode & Decode は何をしますか？
Base64 Encode & Decode はブラウザ上でコンテンツをエンコードまたはデコードするツールで、結果と制限を明確に示します。 検証済みの機能： UTF-8 text encoding, File input up to 50 MB, Base64URL alphabet, Binary download.
Choose Base64URL for URL-safe values
Use standard Base64 for MIME and general byte transport. Use Base64URL for URL components and JWT segments where +, /, and padding are inconvenient.
使い方
- Choose Encode or Decode.
- Enter text, paste Base64, or select a local file; enable the URL-safe alphabet when required.
- Copy text output or download decoded binary bytes.
実際の入出力例
Encode UTF-8 text
入力
Hello出力
SGVsbG8=The five UTF-8 bytes are represented by eight Base64 characters including padding.
一般的なエラーと対処
| 症状 | 原因 | 対処 |
|---|---|---|
| Decode reports invalid Base64. | The alphabet, padding, or copied characters are wrong. | Choose the matching standard or URL-safe alphabet and restore valid padding when required. |
| Decoded output looks corrupted. | Binary bytes are being previewed as UTF-8 text. | Download decoded.bin instead of relying on the text preview. |
Base64 changes representation, not trust
このツール固有の制限： Base64 usually adds about one third to binary size because four encoded characters represent three source bytes. Anyone can decode it without a key.
標準と実装の参考資料
- RFC 4648 — Base-N Encodings (opens in a new tab)Defines Base64 and the URL-safe alphabet.
Base64 — FAQ
Does Base64 encrypt data?
No. Base64 is reversible encoding and provides no secrecy or authentication.
What is Base64URL?
Base64URL replaces + and / with - and _ and commonly omits padding.
Can it encode a file?
Yes. A selected file up to 50 MB is encoded in the current browser tab.
更新内容
実質的な更新： Base64: Added UTF-8 text conversion, local file encoding up to 50 MB, Base64URL mode, validation, copy, and decoded binary download.