These few general questions and answers about the InChI are supplemented by an extensive technical FAQ available here.
1. General InChI Related Questions
1.1 What is InChI?
Originally developed by the International Union of Pure and Applied Chemistry (IUPAC), the IUPAC International Chemical Identifier (InChI) is a character string generated by computer algorithm. It is a tool to be used in software applications designed and developed by those who choose to use it.
The InChI algorithm turns chemical structures into machine-readable strings of information. InChIs are unique to the compound they describe and can encode absolute stereochemistry making chemicals and chemistry machine-readable and discoverable. A simple analogy is that InChI is the bar-code for chemistry and chemical structures.
The InChI format and algorithm are non-proprietary and the software is open source, with ongoing development done by the community. A number of IUPAC working groups is currently creating standard for those areas of chemistry that are not yet handled by the InChI algorithm.
1.2 What is the InChIKey?
The InChIKey has been designed so that Internet search engines (such as Google, Yahoo, Bing, etc.) can search and find the links to a given InChI.
To make the InChIKey the InChI string is subjected to a compression algorithm to create a fixed-length string of upper-case characters. While the InChI to InChIKey hash compression is irreversible, there are a number of InChI resolvers available to look up an InChI given an InChIKey.
1.3 Why do we need the InChI and what is it used for?
The InChI with its associated InChIKey is the only structure representation standard in the public domain, open-source and freely available to the scientific community.
InChIs and InChIKeys are used by scientists, publishers and database providers to enable web-based linking between sources of chemical content whether web-page, journal or magazine, or database.
Several very large databases already have implemented InChI and/or InChIKeys.
1.4 Where can I download the InChI software?
The most current InChI software release can be downloaded from the InChI Trust download page.
1.5 What is the InChI Certification Suite?
The InChI certification suite is a software package developed and designed to check that your installation of the InChI program has been performed correctly. The programs test your installation against a broad set of structures (which are provided with the Suite).
Once the programs are run and the results sent back to the Trust, an “InChI certified” logo will be sent to the respective person or organization. The InChI Trust certification logo can then be put on the pages of the web site for all users to see. The use of the InChI Trust certification logo is optional.
The cost of the InChI certification suite is US $5000 per year.