Base64 Auto Charset

A Sublime Text plugin for Base64 decoding with automatic charset detection (UTF-8, GB18030/GBK/GB2312, Big5, EUC-JP, Shift_JIS, EUC-KR, etc.), and Base64 encoding with GB18030 or UTF-8 charset.

Features

Base64 Decode (with automatic charset detection)

• Automatically detects the charset of the decoded bytes
• Supports UTF-8, UTF-8 with BOM, GB18030/GBK/GB2312, Big5, EUC-JP, Shift_JIS, EUC-KR, and more
• Uses the chardet library for enhanced detection when available (optional)
• Handles Base64 strings with or without padding
• Can replace selection in-place or open result in a new tab

Base64 Encode

• GB18030 Encode: encode the selected text with GB18030 charset, then Base64
• UTF-8 Encode: encode the selected text with UTF-8 charset, then Base64

Installation

Via Package Control (recommended, once accepted)

1. Open the Command Palette (Cmd+Shift+P / Ctrl+Shift+P)
2. Run Package Control: Install Package
3. Search for Base64AutoCharset and install

Manual installation

1. In Sublime Text, go to Preferences -> Browse Packages...
2. Copy the Base64AutoCharset folder into the Packages directory
3. Restart Sublime Text

Usage

All commands are available through the Command Palette. Select some text first (or none, to operate on the entire file), then open the Command Palette with Cmd+Shift+P / Ctrl+Shift+P and type Base64:

The same commands are also available from the main menu under Edit -> Base64 Auto Charset.

Optional key bindings

This plugin does not bind any keys by default, to avoid conflicts with other packages. If you want key bindings, add them to your Preferences -> Key Bindings, for example:

[
    { "keys": ["ctrl+shift+d"], "command": "base64_decode_auto_charset" },
    { "keys": ["ctrl+shift+e"], "command": "base64_encode_gb18030" },
    { "keys": ["ctrl+shift+u"], "command": "base64_encode_utf8" },
    { "keys": ["ctrl+shift+alt+d"], "command": "base64_decode_to_new_tab" }
]

Use cases

Chinese enterprise email / MIME debugging

MIME headers in enterprise email (Subject, From, To, attachment filenames, …) are often Base64-encoded, and the underlying bytes may be GB18030/GBK rather than UTF-8. Select the encoded string and run Base64: Decode (Auto Charset) to get the original text with the correct charset detected automatically:

Subject: =?gb18030?B?xOO6w8rAvec=?=
# select "xOO6w8rAvec=" and run Base64: Decode (Auto Charset)
# -> 你好世界  (detected charset: GB18030)

API response inspection

Base64-encoded payloads returned from APIs can be decoded in place to inspect their original content, regardless of whether the server uses UTF-8 or a legacy Chinese encoding.

Charset detection strategy

Detection order:

1. UTF-8 BOM - check for the \xef\xbb\xbf prefix
2. UTF-8 - try UTF-8, using chardet to disambiguate when non-ASCII bytes are present
3. GB18030 - try GB18030 (a superset of GBK and GB2312)
4. Other CJK encodings - try Big5, EUC-JP, Shift_JIS, EUC-KR in order
5. chardet detection - statistical detection via the chardet library
6. Latin-1 fallback - never fails; used as a last resort

The chardet library is used only when it is already available (e.g. bundled with Sublime Text 4 or installed manually); the plugin works without it, with a slightly reduced accuracy for ambiguous cases.

Privacy

This plugin runs entirely locally. No text is sent to any external service.

Testing

A standalone test suite is provided for the core encode/decode logic:

python3 test_base64_auto_charset.py

48 test cases cover UTF-8 / GB18030 encode and decode, round-trip, Base64 validation, edge cases, real-world email scenarios, and GB18030-specific characters.

License

MIT