CBIN File

What are CBIN files and how to open them

Are you having problems opening a CBIN file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CBIN files.

What is a CBIN file?

A .CBIN file is a CACTVS file.

CACTVS binary format is the native binary representation used by the Cactvs toolkit for storing chemical information such as molecular structures, reactions, and entire datasets. It provides a way to write chemistry-aware data losslessly, including atomic elements, bond orders, stereochemistry, radicals, formal charges, molecular labels, and global dataset metadata. It is intended for situations when complete fidelity of chemical information is needed - for example when exchanging between components of the toolkit, archiving molecules with full annotations, or performing further computation without losing structure.

The format is produced and read by the Cactvs toolkit, which is implemented in ANSI C with scripting interfaces (including Tcl and Python). Writing of this format is automatic when using the standard suffix ".cbin" in file output commands, without needing explicit format specification. It supports writing and reading of structures, reactions, datasets and includes both record-level and dataset-level metadata.

Inside, the format contains both data definitions (such as property definitions and custom types) and the object data itself, so property names, types, and values are preserved. It is lossless with respect to 3-dimensional coordinates, stereochemistry, bond types, and associated metadata. Custom property definitions are handled cautiously: changing a property's type or renaming usually triggers safe behaviour only if the underlying internal layout remains compatible. Other kinds of property definition changes may break compatibility.

The format is binary, containing non-printable bytes, byte values outside standard printable ranges, rather than being line-based or simply ASCII. Common internal field tags include names like A_ELEMENT, A_FREE_ELECTRONS, A_HCOUNT, B_ORDER, R_TYPE, E_NAME, E_IDENT, VERSION, FORMAT among others. The header (at offset 4) often includes a four-byte signature 0x0000000F07; there are recognizable ASCII strings ("CACTVS", field labels) embedded within the file.

How to open CBIN files

Important: Different programs may use files with the CBIN file extension for different purposes, so unless you are sure which format your CBIN file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 31, 2026

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