The IUPAC International Chemical Identifier (InChI)

The IUPAC International Chemical Identifier (InChITM) is a non-proprietary identifier for chemical substances that can be used in printed and electronic data sources thus enabling easier linking of diverse data compilations. It was developed under IUPAC Project 2000-025-1-800 during the period 2000-2004. Details of the project and the history of its progress are available from the project webpage. InChI projects are managed by the InChI subcommittee.

A list of software developers, database providers, and journal publishers incorporating InChI in their products is available here.

The InChITM program version 1.04 is free software developed under the auspices of the International Union of Pure and Applied Chemistry (IUPAC) and the InChI Trust. You can redistribute it and/or modify it under the terms of the IUPAC-InChI Trust License (PDF). This is a more permissive version of the GNU Lesser General Public License version 2.1 that was applied to previous versions of the software.

Download last stable version (1.05) (released Janaury 2017)

See list of InChI Downloads Versions 1.0 – 1.04 here:

IUPAC continues to maintain oversight of InChI development; only systems compliant with the validation protocol (first issued with software release 1.01) are authorised to use the InChI designation. IUPAC welcomes proposals for enhancements. To enable and encourage development of InChI facilities and applications in an Open Source context, a project to encompass this work has been registered with (see, and people wishing to participate should register via the SourceForge web page. There is also a mailing list.

The key publication on the InChI is:
InChI, the IUPAC International Chemical Identifier, by Stephen R Heller, Alan McNaught, Igor Pletnev, Stephen Stein and Dmitrii Tchekhovskoi, Journal of Cheminformatics, 2015, 7:23;
This paper documents the design, layout and algorithms of the IUPAC International Chemical Identifier, InChI.

(older news and journal articles on the Identifier are listed for archives purpose).

The following websites provide the facility to generate InChIs:

    This service works as a resolver for different chemical structure identifiers and allows the conversion of a given structure identifier into another representation or structure identifier.
    Services provide methods to manipulate InChI Strings and InChIKeys, including conversion to and from the MOLfile format, checking validity of the InChI identifiers, searching ChemSpider using InChI inputs etc.
    ACD/Labs’ freely available structure-drawing program ChemSketch includes the facility to generate InChIs from drawn structures.
  • PubChem Server Side Structure Editor v1.8 includes a facility for generating InChIs as you draw the structure.

There are introductory videos on the InChI available on YouTube:

What on Earth is InChI?
The Birth of the InChI
The Googlable InChIKey
InChI and the Islands

For a video about InChI, see Stephen Heller and Stephen Stein at Google Tech Talks on 2 Nov 2006 (1 hr 7 min 18 sec; Flash 7 or higher to watch this video) For presentation slides only, see here.
Abstract : The central token of information in Chemistry is a chemical substance, an entity that can often be represented as a well-defined chemical structure. With InChI we have a means of representing this entity as a unique string of characters, which is otherwise represented by various of 2-D and 3-D chemical drawings, ‘connection tables’ and synonyms. InChI therefore represents a discrete physical entity, to which is associated as array of chemical properties and data…

Also of interest, see Google Tech Talks of 13 Sept 2006 by Peter Murray-Rust, titled ‘The Semantic Chemical Web: GoogleInChI and other Mashups’ (54 min 48 sec)

Stephen E. Stein, Stephen R. Heller, and Dmitrii Tchekhovskoi, An Open Standard for Chemical Structure Representation: The IUPAC Chemical Identifier, in Proceedings of the 2003 International Chemical Information Conference (Nimes), Infonortics, pp. 131-143.

Promotion and extension (project 2004-039-1-800)