To ensure the reliability of the platform for all, Codility has a Concurrent Session Limit which is applied to all customers' accounts.

The Concurrent Session Limit is 100 sessions, meaning a single customer may not have more than 100 sessions in progress at a single moment in time. This helps to keep the platform operational for all customers at all times, as defined in our Fair Use Policy.

What is defined as a session? 

  • A CodeCheck test started by your candidate is one session, active for the duration of time that candidate is completing the test.
  • A demo/practise test started by your candidate when they first open your CodeCheck invite and taken right before they begin their real CodeCheck test is one session, active for the duration of time that candidate is completing the demo/practise test.
  • A CodeChallenge started by your participant is one session, active for the duration that participant is trying to solve the challenge.

What happens if I anticipate hitting the Concurrent Session Limit?

Depending on how high you expect to go, we can slightly increase your specific Concurrent Session Limit for the relevant time period, for example, over the duration of an event. 

  • Expecting more than 50 candidates at once? Contact us at least 1 working day in advance. If you are planning to run an event where you anticipate more than 50 participants to begin a CodeCheck or CodeChallenge session around the same time, please contact us at at least 1 working day before the event. We anticipate some of your candidates/participants may opt to complete a demo/practise test before they begin your CodeCheck or CodeChallenge, and want to make sure that this is prepared for. 

We need to know the following details:

  1. The exact start date/time and end date/time of the event (preferably in UTC)
  2. A link to the CodeCheck test which will be used. If you have not created the test yet, just send us a description of which types of tasks and how many tasks will be used. 
  3. The number of sessions you anticipate beginning around the same time.
  • Expecting more than 150 candidates taking a test at once? We can't support such an increase, please reach out to your Customer Success Manager or if you have any questions.

What happens if I unexpectedly hit the Concurrent Session Limit?

If your account hits the limit and Codility support was not advised in advance, any additional candidates/participants who attempt to begin your CodeCheck test or CodeChallenge will be unable to and will be asked to return 60 minutes later. The limit is counted in real time, so as a session ends, another may be begun immediately. 

If this happens to you and you expect to continue hitting the limit, please contact us at as soon as possible. 

If you have any questions about this or need help, feel free to contact us at

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