The Chemical Probes Portal is an easily accessible online resource for scientists to find and use small-molecule reagents called chemical probes in biomedical research and drug discovery. A unique feature of the Portal is that these molecules are evaluated by recognized chemical probe experts (the Scientific Expert Review Panel, SERP) and recommendations are provided about how to best use these tools in biological research and drug discovery.

Chemical probes are powerful tools for elucidating the role of a target protein in cells and diseases, and are potential pathfinder molecules for drug discovery. However, using compounds incorrectly, or using poor quality compounds, can produce misleading results (Arrowsmith et al., 2015; Antolin et al., 20122). Chemical probes are potent, cell-active, well-characterised small-molecule modulators of protein function. They are mostly inhibitors, but can also be activators, (ant)agonists or degraders or other kinds of modulators, which can be used to perturb a target protein in biological systems. A particular focus lies on the selectivity of a probe to be able to to unpick the activity of that target in cells or in animal models and learn more about the function of its cognate target and its disease relevance. By making it easier for scientists to identify the best tools for their research, the Portal helps researchers make the most of their resources, increasing the reproducibility of experiments, and accelerating research that brings new medicines to patients.

The Portal includes a range of chemical tools, including small-molecule inhibitors, agonists, PROTACs (proteolysis targeting chimeras) molecular glues, and molecular glue degraders. Criteria for well-validated probes can be found on the Criteria for Probes Page.

The Portal also curates a list of historical compounds, which have been used as inhibitors in the past but are no longer considered probes.

Our Scientific Expert Review Panel (SERP) consists of a diverse group of scientific thought leaders from the areas of chemical biology, medicinal chemistry, pharmacology and related disciplines. SERPs provide guidance on the best chemical probes available for a particular experiment and establish best practices for using them. Compounds are rated out of four stars for use in cell systems and in vivo experiments. The Portal recommends probes with three or four stars. Find out more about the star rating system.

How to cite the Chemical Probes Portal

Please cite the following publication:

  • The Chemical Probes Portal: an expert review-based public resource to empower chemical probe assessment, selection and use, Antolin et al.Nucleic Acids Research 2022 gkac909. doi: 10.1093/nar/gkac909
  • add our URL to your publication: www.chemicalprobes.org.

History of the Chemical Probes Portal

Advances in molecular technologies over the past decades have led to unprecedented power to examine molecular mechanisms and pathways across all areas of biology. Alongside biological tools such as RNA interference and CRISPR, biologists rely heavily on the use of small-molecule compounds (inhibitors, agonists, antagonists etc) to probe the specific sites and mechanisms of action in their experiments.

However, the lack of appropriate information accompanying many of these chemical tools has led to an alarming propagation in the use of unsuitable compounds or the improper use of chemical tools.

In 2015, a community call [1] to arms came with an international coalition of experts to alert the research community to the perils of using inappropriate chemical tools in their experiments. The Chemical Probes Portal was born out of an urgent need to enable the wider biological research community about best practices in chemical probe selection, and how to use them appropriately within in-vitro and in-vivo experiments

Despite it being a largely voluntary effort, the Chemical Probes Portal has grown in influence and has been informing biologists for the past >five years. However, it’s growth was hampered due to the lack of sufficient dedicated resources to ensure its progression and adaptation to the ever-changing field of chemical biology.

Recently, the team was awarded a Wellcome Biomedical Resource Award to revitalise, enhance and significantly grow the Chemical Probes Portal. A new dedicated team has been established with the following aims:

  • Significantly grow the number of probes in the portal
  • Reflect changing science
  • Significantly expand the Scientific Expert Review Panel and support them in providing reviews more easily
  • Enhance our training and outreach capabilities
  • Enable more rapid update of information as knowledge changes in the field
  • Enable all of the above through the implementation of a new infrastructure aimed at powering up the data underlying the Chemical Probes Portal


The Chemical Probes Portal is a resource by the Community for the Community. We invite our users to submit new chemical probes or chemical tools for review and inclusion in the Portal. Especially for targets or areas of biology that are still not covered by the site.


Our mission is to provide high-quality recommendations and information about chemical tool compounds for biological research. Help us continue our work.

Supporting Organizations

The Chemical Probes Portal is funded by grant WT212969/Z/18/Z from Wellcome. The Portal is hosted by the Institute of Research, London, and supported by the Structural Genomics Consortium.

Add to our database

Submit new probes and small-molecule tools through our online form.

Join us

Are you an expert in the use of chemical tools? Join our Scientific Expert Review Panel (SERP) .

Spread the word

Get in touch with the team if you want to organise a training session about chemical probes at your institution.