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.BOO file extension

To open .BOO files on Windows, if you expect an archive: try opening the .BOO file with ZipZag (as referenced for BOO archives).

To open a .BOO file, first identify what it is: most often it’s a Kermit BOO-encoded text representation of a binary file, which you “decode” back into the original program. On Windows, a common option for BOO archives is ZipZag; otherwise, view it as text to confirm it looks like Kermit BOO output and then decode using Kermit/BOO tools.

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Last updated: April 29, 2026 · Reviewed by Julian Stricker

Open on your device

Choose your operating system for a dedicated step-by-step opening guide.

How to open .BOO files

Use these platform-specific instructions to open .BOO files safely.

Windows

  1. If you expect an archive: try opening the .BOO file with ZipZag (as referenced for BOO archives).
  2. If it does not open as an archive, open it in a text editor (Notepad, VS Code) and check whether it looks like Kermit BOO text encoding (printable ASCII with an initial line indicating an original filename).
  3. If it appears to be Kermit BOO encoding, use a Kermit/BOO decoding workflow (from the Kermit toolchain for your platform) to convert it back into the original binary file.
Full Windows guide

Mac

  1. Open the .BOO file in a plain-text editor (TextEdit in plain-text mode or a code editor) to determine whether it is Kermit BOO encoded text or Boo source code.
  2. If it is Kermit BOO encoding, decode it using a Kermit/BOO-capable tool on a desktop system (you may need to transfer the file to a system where your Kermit tools are installed).
  3. If it is Boo language source (.boo), open it in a code editor as a normal text file.
Full Mac guide

Linux

  1. Open the .BOO file in a text editor to identify whether it is Kermit BOO encoded text (or Boo source code).
  2. If it is Kermit BOO encoding, decode it using a Kermit/BOO-capable tool available in your environment (from the Kermit toolchain).
  3. If it is Boo source code, treat it as a text file and open it in your preferred editor.
Full Linux guide

iOS

  1. iOS typically won’t decode Kermit BOO or BOO archives directly; open it in the Files app to preview as text (if possible), then transfer it to a desktop system to decode or extract it with appropriate tools.
Full iOS guide

Android

  1. Android typically won’t decode Kermit BOO or BOO archives directly; try viewing it as text in a file viewer, then transfer it to a desktop system to decode or extract it with appropriate tools.
Full Android guide

Security notes

  • Kermit BOO files are commonly used to distribute binary programs; after decoding, the output may be an executable. Treat the decoded file as untrusted until you know its origin and purpose.
  • Because .BOO is plain text, it is easy to disguise content; confirm whether you have a Kermit BOO encoding, a BOO archive, or a source code file before using tools that will execute or extract content.
  • Be cautious with extraction/decoding tools on malformed inputs: corrupted or intentionally crafted encoded text can trigger bugs in parsers; prefer well-known, maintained tooling from the Kermit ecosystem when working with Kermit BOO files.

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Can't open this file?

These are the most common causes and fixes when .BOO files fail to open.

Common reasons

  • The .BOO file opens as gibberish or won’t “run”
  • An archive tool says the .BOO file is not a supported archive
  • Decoded output is corrupted or the filename is wrong
  • Confusion with Boo programming language files (*.boo)

Fix steps

  1. Open the file in a text editor and confirm it is printable ASCII and appears to be a Kermit BOO encoding (often with an initial line indicating the original filename).
  2. Use a Kermit/BOO decoding tool to convert it back into the original file, then open/run the restored file with the correct program for that file type.

OS-specific troubleshooting

What is a .BOO file?

.BOO (Kermit “boo”) is a compact, plain-text, printable encoding for distributing binary files through text-only channels. The Kermit user guide describes it as a 4-for-3 (6-bit) encoding with null compression, and the first line includes the original filename. Because it is plain text, it was historically useful for mixing text and binary on media like tapes and for cross-system software distribution.

Background

In Kermit documentation and archives, “BOO” refers to a bootstrap/printable encoding used to ship binary programs in a form that can survive text-only transfers. The Kermit User Guide describes its structure and encoding approach (including 4-for-3 6-bit encoding and null compression), and notes that the first line carries the original filename so the decoder can restore it.

The Kermit Project archive notes .boo files were used as a compact plain-text encoding of binaries, particularly useful when text and binary had to coexist (for example, when distributing collections of files on tape). For classic systems, OS/8 Kermit documentation describes an encoder that converts OS/8 files into printable ASCII “.BOO” format, and mentions it as a common distribution format for Columbia Kermit files.

Separately, some modern references treat .BOO as an ASCII-encoded compressed archive (and list ZipZag on Windows as an opener). Also note that .boo is widely recognized in developer tooling as the Boo programming language source extension; in that case it’s just a text code file, not a Kermit-encoded binary.

Common MIME types: text/x-boo

Further reading

Authoritative resources for more details on the .BOO format.

Common .BOO issues

The .BOO file opens as gibberish or won’t “run”

Kermit BOO files are meant to be decoded back into the original binary; viewing them directly shows encoded text, not the usable program.

  1. Open the file in a text editor and confirm it is printable ASCII and appears to be a Kermit BOO encoding (often with an initial line indicating the original filename).
  2. Use a Kermit/BOO decoding tool to convert it back into the original file, then open/run the restored file with the correct program for that file type.

An archive tool says the .BOO file is not a supported archive

.BOO is not universally an “archive”; it may be Kermit BOO-encoded binary or a different .boo usage such as source code.

  1. Try opening it as plain text to determine whether it is Kermit BOO encoded text or Boo source code.
  2. If you specifically expected a BOO compressed archive, try ZipZag on Windows (commonly referenced for BOO archives); otherwise use Kermit BOO decoding instead.

Decoded output is corrupted or the filename is wrong

BOO decoding depends on intact text content; line-ending changes, truncation, or copy/paste transfers can break the encoding. The original filename is typically stored in the first line of the BOO file.

  1. Re-download or re-transfer the .BOO file using a method that preserves the exact text (avoid copy/paste; use file transfer).
  2. Ensure the decoder is treating the input as text and that the first line (original filename line) is intact before decoding again.

Confusion with Boo programming language files (*.boo)

Some systems associate .boo with the Boo programming language (a text source file) and may not recognize it as Kermit BOO encoding.

  1. Open the file in a text editor: Boo source looks like normal code, while Kermit BOO is an encoding block intended for decoding to a binary.
  2. If it is code, keep it as text and use developer tooling; if it is Kermit BOO, use a BOO decoder workflow instead of code tools.

FAQ

Is .BOO a document file?

Usually no. The most common meaning in Kermit documentation is a printable ASCII encoding of a binary file (meant to be decoded), not a human-authored document format.

How can I tell whether my .BOO is Kermit BOO encoding or something else?

Open it in a text editor. Kermit BOO is printable ASCII meant for decoding and typically includes an original filename in the first line; Boo programming language files look like normal source code; some .BOO files may be treated as ASCII-encoded compressed archives by specific tools.

Can I convert a .BOO file by renaming the extension?

No. If it is Kermit BOO, you must decode it to restore the original binary. If it is an archive, use an archive tool that supports that specific BOO format.

What MIME type is associated with .boo?

Some MIME registries and developer tooling map .boo to text/x-boo (commonly used for Boo language source files). This does not necessarily describe Kermit BOO-encoded binaries.

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