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checkCIF is the web validation service of the International Union of Crystallography (IUCr). You upload a crystal structure report in Crystallographic Information File (CIF) format, and the service returns a report of alerts about the data and the model. In chemistry and the wider structural sciences, running a CIF through checkCIF before submission is a routine step in scholarly publishing.
What is checkCIF?
The IUCr describes checkCIF as a service of the Union, and its input page asks for a CIF file. The CIF format was described in 1991 by Hall, Allen and Brown as a standard for exchanging crystallographic data. A CIF carries the numerical results of a structure study together with supporting experimental data and details of the procedures used.
According to Spek (2026), checkCIF started with tests of whether the supplied data are complete and whether their values fall within the expected range. Today the PLATON software carries out most of the tests in the checkCIF framework. Problems are reported as a set of ALERTS, each with a short clarification.
Who runs checkCIF and what does it cover?
The service is operated by the IUCr. Its input page lists sponsors including IUCr Journals, the Cambridge Crystallographic Data Centre (CCDC), the American Chemical Society, Elsevier, Wiley, the Royal Society of Chemistry, Crystals (MDPI) and IUCrData. Its options include a CCDC duplicate check, which you can switch on or off on the input page.
Beyond completeness and range tests, the underlying PLATON tools can flag issues such as missed twinning, missed additional symmetry and voids. Spek notes that a locally installed PLATON gives more detail on these issues than the alert text in the report.
How do you use checkCIF?
The labels below are those shown on the checkCIF input page. Check the page itself for the current wording.
- Open the service: go to https://checkcif.iucr.org/.
- Choose the file: use the File name field to select your CIF.
- Select the report form: choose HTML, PDF, or PDF email. The page recommends PDF email for CIFs that might take a long time to check. To receive the report by email, enter your address in the email field.
- Select the validation type: the options are Full validation of CIF and structure factors, Full IUCr publication validation of CIF and structure factors, and Validation of CIF only (no structure factors).
- Set the Validation Response Form (VRF) output: under Output Validation Response Form pick Level A alerts only, Level A and B alerts, Level A, B and C alerts, or None.
- Set the duplicate check: under Output CCDC’s duplicate check choose Yes or No.
- Submit and read the report: the IUCr help page says alerts are advisory, but you should always attempt to resolve as many as possible of the alerts in all categories.
Your journal may add its own requirements, so follow its author instructions during the manuscript submission process.
Strengths and limits of checkCIF
Strengths:
- It gives authors, editors and reviewers one shared set of automated checks on a structure report.
- It tests completeness and whether values fall within the expected range, before a paper goes out for review.
- It is reached through a web browser and needs no local installation.
Limits:
- Alerts are advisory. A person still has to judge each one, and Spek notes that some alert messages are informative and do not necessarily need a comment.
- The alert text is short. For detail on twinning, symmetry or voids, a local PLATON run gives more.
- The online service needs a CIF as input, and the validation types that include structure factors need those data to be supplied.
What are the alternatives to checkCIF?
checkCIF is a web service, while PLATON can be installed locally. Because PLATON performs most of the tests used by checkCIF, running it on your own machine is a way to look more closely at a flagged issue. The two complement each other.
| Tool | Maintainer | How you run it | Role |
|---|---|---|---|
| checkCIF | IUCr | Web service | Validation report on an uploaded CIF |
| PLATON | Anthony L. Spek | Local installation | Carries out most of the checkCIF tests and gives more detail on issues such as twinning and voids |
For related chemistry workflows, see electronic lab notebooks for chemistry, chemistry manuscript writing conventions and the PubChem bioassay data repository.
Frequently asked questions
What is a CIF file?
A CIF (Crystallographic Information File) is the standard format for exchanging crystallographic data, described by Hall, Allen and Brown in 1991. It holds the numerical results of a structure study and supporting experimental details. checkCIF takes a CIF as its input.
Are checkCIF alerts errors I must fix?
The IUCr help page calls alerts advisory, and asks you to attempt to resolve as many as possible in all categories. Spek adds that alerts should be addressed with a correction where applicable, or a short explanation of a special situation.
What is a Validation Response Form?
It is an output option on the checkCIF input page. You choose whether it covers Level A alerts only, Levels A and B, Levels A, B and C, or none. Ask your target journal how it wants alerts answered.
Do I need structure factors to use checkCIF?
No. The input page offers Validation of CIF only (no structure factors) as well as two validation types that include structure factors.
Sources
All sources were checked on 2026-11-07.
- International Union of Crystallography. checkCIF service: https://checkcif.iucr.org/ and help page https://checkcif.iucr.org/help.html.
- Spek, A. L. (2026). On the SHELX, PLATON and IUCr/checkCIF crystal structure validation platform. Acta Crystallographica Section C: Structural Chemistry, 82(10), 595–602. https://doi.org/10.1107/s2053229626009319
- Hall, S. R., Allen, F. H., & Brown, I. D. (1991). The Crystallographic Information File (CIF): a new standard archive file for crystallography. Acta Crystallographica Section A, 47(6), 655–685. https://doi.org/10.1107/S0108767391006864
