Base64デコーダー - テキストとファイルデコード
ツールに戻るAbout Base64 Decoding
Base64エンコードされた文字列を元のテキストまたはバイナリデータにデコード。メール添付ファイル、データURL、APIレスポンス、暗号化されたデータ送信に不可欠。テキストとファイルコンテンツを処理。
Decode Features
- Instant Base64 to text conversion
- Automatic validation and error detection
- Handles malformed Base64 gracefully
- Supports both standard and URL-safe Base64
When to Use Base64 Decode
- Processing API authentication tokens
- Analyzing email attachment data
- Debugging encoded web data
- Converting data URLs back to readable format
Important: Only decode Base64 from trusted sources. Decoded content may contain executable code or malicious data.
Base64 Decoding Examples
Simple Text Decoding
入力:
SGVsbG8gV29ybGQh出力:
Hello World!HTTP Basic Auth Decoding
入力:
QWxhZGRpbjpvcGVuIHNlc2FtZQ==出力:
Aladdin:open sesameJSON Data Decoding
入力:
eyJuYW1lIjoiSm9obiIsImFnZSI6MzB9出力:
{"name":"John","age":30}URL Decoding
入力:
aHR0cHM6Ly9leGFtcGxlLmNvbS9wYXRo出力:
https://example.com/pathBase64 Validation Guide
Learn how to identify valid Base64 encoded strings:
- Contains only A-Z, a-z, 0-9, +, /, = characters
- Length is multiple of 4 (with padding)
- Padding (=) only appears at the end
- Maximum 2 padding characters
Common Issues & Solutions
Invalid Base64 Characters
Remove or replace invalid characters. Only use Base64 alphabet.
Incorrect Padding
Ensure proper = padding at the end (0, 1, or 2 characters).
Garbled Output
Check character encoding. Source might be corrupted or partially copied.
How Base64 Decoding Works
- 1 Convert Base64 characters to 6-bit values
- 2 Combine 6-bit values into 8-bit bytes
- 3 Handle padding and create binary output
- 4 Convert binary to text/data format
Padding Information
= - One missing byte== - Two missing bytesNo padding - Perfect alignment