Codility Test: Format, Scoring and How to Prepare | Cohesyve

Codility is a platform companies use to screen developers with coding tasks. Each employer picks the tasks, the languages and the time, and can give some tasks more points than others. Codility answers candidates' questions about how its tests work in a public FAQ. This guide brings those answers together, with advice on preparing.

What is a Codility test?

Codility describes its screening assessments as tests of job-related technical skills. You'll be asked to solve several problems by writing code, changing existing code or answering technical questions. Most tasks are short programs, usually 10 to 20 lines, and they vary in difficulty. Your answers are scored automatically and the results go to the employer.

How long is a Codility test?

Typically between half an hour and two hours. The employer sets the exact limit, which depends on the number of tasks.

The timer covers the whole assessment, not each task.
You can look before you start. Opening the invitation link shows the introduction, the employer's policies, the number of tasks, the time and the languages allowed. Until you press Start, you can leave and come back.
Once you start, you can't pause. Plan to finish in one sitting, and start within the employer's testing window.
Speed doesn't earn points. Codility says its tests allow plenty of time, and the time you take doesn't factor into automated scoring.
When time runs out, whatever code is in the editor is submitted automatically.

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How Codility scores your code

Codility runs your submitted code against a set of test cases after you finish. It checks two things:

Correctness: whether your code gives the right answers, including corner cases.
Scalability or performance: whether it stays practical as inputs grow. This applies to algorithmic tasks.

Three rules follow from that, all from Codility's FAQ:

Code that doesn't compile scores nothing. Use the Run button often. Codility auto-submits at the end, so keep a compiling version at all times.

Passing the example isn't passing the task. Clicking Run and getting "OK" only shows that your code compiles and handles the example case. The example isn't part of the scored tests, so you can pass it and still score 0%. The exception is Codility's "real-life" tasks, which list every requirement and tell you how many test cases you passed.

You earn points per test passed. Each submitted solution earns points as it passes the unit tests that check the task's requirements.

Tasks may not count equally. By default every task carries the same weight, but an employer can weight them differently. If it has, the test tells you, so you can plan your time.

Coding style usually doesn't affect the automated score, though some tasks are designed to assess it, and the employer may review your code by hand.

The rules

Work alone. Codility says you may not consult or get help from other people. Whether you can use other resources, such as documentation, depends on the employer's policy shown on the test link.
Your own IDE, only if permitted. If the employer allows it, you can write in your own editor and paste the solution back. Run it in Codility to check it compiles, since its compiler may differ from yours. The supported language version is shown in the interface.
Standard libraries only, unless the task says otherwise.
Keep the function signature exactly as given. You can add helper functions and imports. Some tasks limit how much of the starting code you may change, to test how few edits you need.
No need to validate inputs. Codility says you don't have to check that the task's stated assumptions hold.
Camera or screen sharing, if required. Some employers require them; the test link tells you, and you'll be asked to allow access.

What a Codility task looks like

Codility publishes practice tasks in its lessons, and employers choose from a larger library. This is our own illustration of the style. It is not a Codility task.

Our example: Given an array of integers, return the length of the longest run of consecutive equal values. For [4, 4, 1, 1, 1, 7], the answer is 3. The array can hold up to 100,000 values.

A correct but slow solution compares every pair and fails the performance tests on large arrays. A single pass that tracks the current run and the best run so far passes them. Correctness tests would also check an empty array, an array of one value, and an array where every value is the same.

Before you start

Use a laptop or desktop. Codility isn't supported on phones or tablets.
Use a supported browser: Chrome 131+, Edge 130+, Firefox 132+, Opera 114+ or Safari 17+. Recording and screenshot features work only in Chrome, and screen sharing needs Chrome, Edge or Opera.
Check whether you need the Codility app. If your assessment needs it, opening your invitation link takes you to a page asking you to download it. The app runs on macOS and Windows only, so if you use Linux, contact the employer before you start. Otherwise nothing needs installing.
Your code saves automatically. If the browser closes, you resume where you left off. You can move between tasks freely before submitting each one; after you submit a task, you can't change it.
Ask for adjustments. Codility's platform meets WCAG 2.2 AA, works with screen readers and keyboard navigation, and has an accessibility mode with up to 400% zoom. Tell the employer if you need extra time.
If you lose your connection, tell the employer straight away and ask them to reopen your session. It's their decision.

Will I see my results?

Only if the employer chooses to share them. If you don't see results straight after the test, the employer has kept them confidential.

How to prepare

Take Codility's demo test. It shows the editor, the Run button and how custom test cases work, so none of it is new on the day.

Work through Codility's lessons. Codility publishes free lessons with practice tasks, grouped by topic and starting with iterations. Each task can be started and solved in the browser.

Add your own test cases. Codility lets you add test inputs in the editor. Use it: empty input, one element, all equal values, negative numbers, the largest allowed size.

Think about scale before you code. Read the input limits. If an array can hold 100,000 values, a solution that compares every pair is likely to fail the performance tests.

Keep it compiling. Run after every meaningful change. A brilliant solution that doesn't compile at the buzzer scores zero.

Where Cohesyve fits

Codility scores the code you submit automatically, against test cases. Cohesyve, which publishes this guide, runs practice job simulations of a role's real work, for roles such as backend developer, full-stack developer and QA engineer, with a report on where you lost marks. It isn't a Codility practice test. For other platforms, see our guides to Coderbyte, HackerRank and the CodeSignal GCA.

Sources

Checked 21 October 2026.