RXN File

What are RXN files and how to open them

Are you having problems opening a RXN 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 RXN files.

What is a RXN file?

A .RXN file is a MDL Reaction Format file.

MDL Reaction Format (.rxn) is a plain-text format used to record single chemical reactions by listing reactants, products, and optionally agents (substances involved in the reaction but not directly transformed). Files are created by chemistry software that work with MDL's reaction formats (often called RXN files), typically when a user draws or defines a reaction in a molecular editor. Its main use is to save the structural details of one reaction - what enters, what leaves, and how the molecular structures connect - so other chemistry tools can import, display, simulate, or use it in reaction databases.

These files embed full molecular structure blocks for each participant using the same atom, bond, coordinate, and property syntax found in MDL Molfile files, allowing details like atom types, bond orders, 2D or 3D coordinates, and mapping between atoms in reactants and products. They support two major variants: V2000 (the older, simpler form) and V3000 (which handles more complex cases, such as large molecules, many atoms or bonds, and the inclusion of "agent" molecules). Once created, files are read by drawing tools, analyzers, or cheminformatics software to reconstruct or manipulate the reaction.

Files begin with the ASCII signature "$RXN" at the start of the first line, followed by a header block, then a line giving counts of reactants, products, and optional agents. After that each molecule is represented by a block starting with "$MOL" and the full Molfile content. Internal keywords include "$RXN" and "$MOL", and in V3000 variant also structural keywords like "M V30 COUNTS", "M V30 BEGIN REACTANT/PRODUCT/AGENT", "M V30 BEGIN CTAB", "M V30 BEGIN ATOM", "M V30 BEGIN BOND", etc.

How to open RXN files

We have identified one RXN opener that is compatible with this specific type of RXN file.

Programs that open MDL Reaction Format files

Last updated: August 13, 2026

Various apps that use files with this extension

These apps are known to open certain types of RXN files. Remember, different programs may use RXN files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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