What is the B file format?
A .b file is a Lotus Applause Batch List - a small auxiliary data file produced by the Lotus Applause presentation software during the DOS and early Windows era of the 1980s and 1990s. Lotus Applause was a slide-show and business-presentation product developed by Lotus Development Corporation (later acquired by IBM), sold alongside flagship titles such as Lotus 1-2-3.
The file stores a simple ordered list of items that the Applause application processed in batch mode - for example, slide or resource filenames that the program would load or export in sequence. The internal structure is not publicly documented, and no formal specification was ever released by Lotus or IBM. Files are plain text (ASCII), carry a text/plain MIME type, and carry no embedded file-signature bytes, meaning format identification relies entirely on knowing the source application.
The single-letter .b extension is heavily overloaded in computing: unrelated uses include B-language source code, plain-text fragments, and backup markers. A .b file encountered outside a legacy Lotus environment is unlikely to be an Applause batch list. The creating application is the only reliable identification method.
Lotus desktop products - including Applause - were discontinued by IBM through the 2010s. Files can be opened with any plain-text editor such as Notepad++ or VS Code, although no modern software re-creates the original batch-processing workflow.
Security & safety
RISK: LOWA .b file is data, not a recognized executable type, so it's low risk to inspect - opening it in a text editor (or running file on it) is safe and is the right first step to find out what it really is. The only caution is the usual one for unknown files from untrusted sources: don't rename a mystery .b to an executable extension and run it, and be wary of 'universal .b openers' on download sites, which tend to be adware bait for such an ambiguous extension.
Format details
in a nutshell- Source code file (BASIC / Brainfuck / Limbo / Befunge) - Several programming languages use .b for source files - e.g. Limbo (Inferno OS), and informally Brainfuck/Befunge/BASIC; these are plain-text code, opened in a text editor or the language's tools.
- Generic backup / part file - Some tools append .b as a backup or sequence marker; such a file is just a copy of another file and opens as whatever its original type was.
- Grand Theft Auto save / misc data - A few games and utilities have historically used .b for save or data files; format depends entirely on the creating program.
Programs that open B files
Windows2 apps
Text editor (Notepad++, VS Code)
Open-source Open the .b in a text editor first - if it's a batch list, source code, or any text file, you'll see its contents and can identify it.
Lotus 1-2-3 (legacy)
Paid Only relevant for genuine legacy Lotus data; Lotus 1-2-3 is discontinued (end of support 2014) - use a modern spreadsheet/text tool instead. 
macOS1 app
Text editor (BBEdit, VS Code)
Free Open the .b as text to inspect its contents and identify the actual format. 
Linux1 app
Text editor (any) / file command
Open-source Run file yourfile.b to detect the type, then open it in a text editor if it's text. Technical details
deep spec| Developer | Lotus Development Corporation (acquired by IBM in 1995) |
| Associated application | Lotus Applause - DOS/Windows slide-show and business-presentation tool |
| Primary role | Ordered batch list defining a sequence of items (e.g. slide or resource filenames) for automated in-application processing |
| Encoding | Plain text, ASCII |
| MIME type | text/plain |
| Compression | Uncompressed |
| Encryption | Unencrypted |
| File signature (magic bytes) | No embedded header signature; file type identified by application context only, not by byte pattern |
| Typical file size | A few bytes to a few kilobytes (small list file) |
| Operating system | DOS / early Windows (legacy era) |
| Extension collision risk | High - .b is also claimed by B-language source code, plain-text fragments, and backup stubs from entirely unrelated software |
| Byte order | Not applicable - character-based plain-text content |
| Internal structure documentation | Undocumented; no public specification was issued by Lotus or IBM |
| Product status | Discontinued - Lotus Applause was retired along with the broader Lotus desktop portfolio by IBM during the 2010s |
| Identification method | Application origin (the program that created the file) is the only reliable identifier; no signature or header field exists |
| Released | Lotus desktop software era (1980s-1990s) |
| Latest version | N/A (legacy; Lotus desktop products discontinued by IBM in the 2010s-2020s) |
B conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about B files.
Frequently asked questions
What is a .b file?
How do I open a .b file?
file yourfile.b on macOS/Linux to detect the type. If it's source code, open it in the matching language environment; if it's a backup, rename it to the original extension.
