The Codility test: what your score actually measures
Most people fail a Codility test believing they passed it. The examples in the task statement all printed the right answer, the editor said OK, the submission went through — and the report came back at 40%. The reason is simple and it is worth knowing before you sit one: the examples you can see are not part of the score.
Codility test: quick answers
What is a Codility test?
A timed, machine-graded coding assessment that an employer sends before an interview. Each task is scored on hidden test cases (correctness) and, where it matters, on performance.
How is a Codility test scored?
As the percentage of hidden assessed test cases your code passes, plus a separate performance grade. The examples printed in the task are not assessed, and how fast you finish does not enter the automated score.
How long is a Codility test?
The employer sets the limit; Codility says assessments typically last between half an hour and two hours. One timer covers the whole test and cannot be paused.
Is a Codility test proctored?
Only if the employer switches proctoring on for that test (tab-switch flags, webcam snapshots). Every report still shows a timeline of time out of focus and pasted text, plus a Similarity Check.
What is a passing Codility score?
There is no universal pass mark. Codility sets no Passing Score by default; the employer chooses one for each test.
Can I Google during a Codility test?
Only if the employer allows it. Codility's rule is that you work on your own and may not consult other people; whether books, websites or other resources are permitted is set by the company in the assessment policies included in your test link. If they are unclear, ask your test administrator before you start.
What the score is actually made of
Every task is graded on two separate axes, and they are reported separately.
- Correctness — the share of hidden test cases where your output matches the expected one. A task runs at least six assessed cases, and your task score is the percentage of them that pass. The examples shown in the statement are demonstrations, not assessed cases.
- Performance — whether the solution stays inside the time and memory limits as the input grows. This applies only to tasks where scalability is part of the point, and it is graded even when your answers are all correct.
That second axis is the one people do not plan for. A correct O(n²) loop on a task designed around O(n log n) returns the right answer on every case it finishes and still loses most of the performance points, because the large cases time out.
What is on a Codility test: task types
The employer builds the test from Codility’s task library, so the number and mix of tasks are theirs to choose; the test intro page lists them before the timer starts. Most invitations draw on two kinds of task.
- Algorithmic tasks. A short problem statement, a function signature and a constraints block. These are the tasks scored on correctness and performance as described below, and they are usually available in many languages, so you pick the one you are fastest in.
- Real-life, technology-specific tasks. A small project in one framework, such as Spring, Django, Flask, Node.js, Laravel, Ruby on Rails or ASP.NET Core, where you fix or extend existing code. Codility’s own guidance for hiring backend developers is to pair one of these with a short fundamental task, and to add an SQL or Bash task where it fits the role.
One rule applies to both: unless the task description says otherwise, you may only use the standard libraries and imports of the language. A solution built around a third-party package you are used to will not run.
Typical Codility tasks and how to practise them
Codility publishes its own free training set, Codility Lessons, and it is the closest thing to the house style. On 9 November 2026 it had 17 lessons, each with a short reading PDF and graded tasks: iterations, arrays, time complexity, counting elements, prefix sums, sorting, stacks and queues, leader, maximum slice, prime and composite numbers, the sieve of Eratosthenes, the Euclidean algorithm, Fibonacci numbers, binary search, the caterpillar method, greedy algorithms and dynamic programming.
Use them the way the test will score you. Solve each task against the clock, submit, and read which hidden cases failed before you look anything up. Prefix sums, counting with a hash map and two pointers (the caterpillar method) come up again and again across the Lessons, so drill them until the O(n) version is the first one you write. If you have only a week, start with lessons 1 to 9 and leave dynamic programming and the number-theory lessons for last.
Read the constraints as a complexity budget
The constraints block is not decoration. It is the task telling you which complexity it will accept, and it is the single most useful thing on the page.
- N up to 100,000 or more — anything quadratic will time out. You are being asked for sorting, a hash map, two pointers, or a prefix sum.
- N up to a few thousand — O(n²) is usually fine, and reaching for something clever costs you time you will need elsewhere.
- Values up to 2 billion — the task is telling you that a 32-bit accumulator will overflow. In a language where that matters, it matters here.
Work out the target complexity before you write a line. On a machine-graded test there is nobody to award marks for a good instinct you never implemented.
Where the points actually go
Three patterns account for most of the lost score, and none of them are about algorithmic ability.
- Edge cases nobody tested. Empty input, a single element, all elements equal, the minimum and maximum allowed values. These are exactly the hidden cases, because they are the cheapest ones to write.
- Off-by-one at the boundary. Inclusive versus exclusive ranges cost more Codility points than any data structure.
- Running out of time on task three. The timer covers the whole test, not each task. A person who leaves a working brute force on every task usually outscores a person with one perfect solution and two blanks.
Partial credit is real, so use it
Because the score is a percentage of cases, an honest brute force is worth a great deal more than an empty editor. The sequence that scores best under time pressure is almost always the same: write the obvious solution, submit it, then optimise it and submit again. You bank the points first and improve them second.
If you know your solution is too slow and you cannot fix it, leave it. A timed-out submission on the large cases still collects every small and medium case it passes.
The last ten minutes
Stop writing new code. Run each task once with an empty input, once with a single element, and once with the largest value the constraints allow. That pass finds more points than a fourth attempt at the hard task, and it takes three minutes.
One more thing worth knowing rather than discovering afterwards: the platform records what happens in the tab, including focus changes and pasted blocks, and the employer sees that summary next to your score. Plan your test as something you sit and finish, not something you assemble from other windows.
Is Codility proctored? Webcam, screen and video
Only if the employer turns it on. Proctoring is a per-test setting, so two Codility invitations can look identical and still be monitored very differently. Your test intro page tells you what this one uses before the timer starts.
- Webcam snapshots. Pictures taken at regular intervals and when a proctoring event is flagged, kept for 30 days and shown in the candidate report.
- Screen proctoring. Optional. You are asked to share a tab, a window or your entire screen, and what you share is recorded.
- Video proctoring. Optional. A recording of the whole session appears in the report after you finish.
- Behavioural events. Leaving the tab, pasting and similar events are logged on a timeline next to your code.
Codility is not supported on phones or tablets, and that matters most when a test uses video or screen proctoring — sit it on a laptop or desktop with a supported browser and a working camera.
Codility at Microsoft and other employers: whose pass mark is it?
The employer’s. Codility has no default Passing Score; whoever builds the test sets one, picks the tasks and the time limit, and decides how the report is used. Microsoft has not published a cut-off for its Codility assessments, so any single number you read for “the Microsoft Codility passing score” is a guess.
What does carry over from company to company is how the score is built: hidden test cases, performance tests on the larger inputs, and partial credit for every case you pass. A clean solution that passes every printed example can still score low, and a high score is usually one input into a recruiter’s decision rather than an automatic invitation — which is why candidates sometimes hear nothing after a test they believe they aced.
So prepare for the format, not for a rumoured number: bank a correct brute force on every task first, then spend the remaining time on the complexity the constraints demand.
What Codility's own help centre confirms
- Length. The employer sets the time limit. Codility says assessments typically last between half an hour and two hours, and the limit is shown on the test intro page linked from your invitation.
- One timer. The time on screen is for the whole assessment, not for a single task, and it cannot be paused once you start.
- Speed is not scored. How fast you finish does not factor into the automated score — only the test cases do.
- When time runs out, the code in the editor is submitted automatically, but it has to compile to be evaluated. Keep every task in a compiling state, not only the one you are working on.
- “OK” after Run only means the code compiled and returned the right result for the example test case.
- What the employer sees. A timeline for each task showing time in and out of focus and text pasted into the editor, plus a Similarity Check that compares solutions with more than 12 million other submissions, solutions leaked online and AI-generated solutions. Proctoring — tab-switch flags, webcam snapshots — is an option the employer switches on per test. Codility itself notes that a paste does not by itself mean cheating.
For the integrity side, see can Codility detect AI.
Sources
- Codility Support — Automated Scoring Principles
- Codility Support — Reading a candidate test report
- Codility Support — How much time does a Codility assessment take?
- Codility Support — What if I run out of time?
- Codility Support — I clicked “Run” and the app said “OK”
- Codility Support — How do I set a Passing Score?
- Codility Support — Similarity Check and what to do
- Codility Support — Assessment Integrity Features
- Codility Support — Video Proctoring
- Codility Support — Proctoring: Behavioral Events Detection
- Codility Support — What browsers are supported?
- Codility Support — May I consult a book, website, or colleague?
- Codility Support — Which libraries can I use?
- Codility Support — Assessing Backend Developers (task types)
- Codility Lessons — free training tasks
Every factual claim above was checked against these official pages on 14 October 2026 (the rule on outside resources on 26 October 2026, proctoring options on 5 November 2026, task types, libraries and the Lessons list on 9 November 2026). Vendors change their rules, so check again before your test.
FAQ
Do the examples in the task count towards my Codility score?
No. The examples in the statement are illustrations. Your score is the percentage of hidden assessed test cases your solution passes, which is why a solution that handles every printed example can still score low.
What is a passing Codility score?
There is no universal pass mark. Codility sets no Passing Score by default — the employer chooses one for each test, and the report lets them rank candidates by the overall score, which combines correctness and, where measured, performance.
What score do you need on the Microsoft Codility test?
Microsoft has not published one. On Codility the employer sets the Passing Score for each test — there is no default — and the score is usually one input into the recruiter’s decision, not an automatic pass. Aim to pass every hidden case you can, starting with a correct brute force on each task.
Can I go back to an earlier task?
Yes. The timer covers the whole assessment rather than each task, and you can move between tasks until it runs out. That is exactly why banking a brute force early and returning to optimise it works so well.
Does Codility detect tab switching or pasted code?
The report shows a timeline for each task with time out of focus and text pasted into the editor, and a Similarity Check compares solutions with other submissions, solutions leaked online and AI-generated ones. Webcam snapshots and tab-switch flags only appear if the employer enabled proctoring. Nothing fails you automatically — Codility itself says a paste is not proof of cheating — but the employer sees it all next to your score.
Does Codility record your screen or webcam?
Only when the employer enables it for that test. Webcam proctoring takes snapshots at intervals and when an event is flagged, kept for 30 days; screen proctoring records the tab, window or screen you choose to share; video proctoring records the whole session. Your test intro page says which of these apply.
How long is a Codility test?
The employer sets the limit; Codility says assessments typically take between half an hour and two hours. The timer cannot be paused, the time you take does not affect the automated score, and when it runs out the code in the editor is submitted automatically — it must compile to be evaluated.
Can I Google during a Codility test?
Only if the employer permits it. Codility requires you to work on your own and not consult other people; whether you may use books, websites or other resources depends on the assessment policies included in your test link. If the policy is unclear, ask your test administrator before you start.
What kind of questions are on a Codility test?
Mostly algorithmic tasks scored on hidden test cases for correctness and performance, and, for some roles, technology-specific tasks in a framework such as Spring, Django or Node.js, sometimes with an SQL or Bash task. The employer picks the mix; the test intro page lists the tasks before the timer starts. Codility Lessons, its free training set, shows the house style.
Can I use external libraries on Codility?
Only if the task description says so. Otherwise Codility allows only the standard libraries and imports of the programming language supported in that task.