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The Reply Hack the Code Challenge is an online coding and security competition open to coders aged 14 to 19 years the day of the challenge (12th March 2025), from all over the world.
I’m aged between 16 and 19. Which challenge can I take part in?
You can choose the challenge you prefer based on your coding and security skills. To see if the level of the challenge is right for you, take a look at the code challenge Past editions and CTF past editions, level 100.
No. To play on 21st March, you need to join a team, create your own, or join the random queue. By registering on the platform, you’ll get updates on upcoming online challenges.
No, this coding challenge is completely free!
You can register until 11th March, 23:59pm, CET.
Once you’ve registered, you can join a team or form one. Alternatively, you can join our Discord Server in order to find participants to play with.
To update your details at any time, log in to your profile and click “Edit profile”.
Please send your cancellation request to challenges@reply.com.
To form your team, log in to the Reply Challenges platform, click the “Team up” button and select “Create new team”. Once you’ve formed a team, you’ll see it when you log in to the platform. You can also choose a team name and invite your friends. Just fill in their email addresses and send the invitation. Remember, Replyers play a challenge reserved for them. Mixed teams are not allowed.
Your team can have 1 - 6 people.
No problem. You have until 11th March at 23.59 to join someone else’s team. You can look for team members sharing your skills both on your profile or on Discord.
No, but you are free to leave your current team. They won’t receive any notification, so remember to tell them.
No, the challenge is open to individual students. They will need to register as an individual, and then form a team made of 1 - 6 members. On a voluntary basis, the team can choose to join the High School League, adding the name of the school while forming the team.
No, teams can be in different towns, cities or countries during the challenge.
No, but it could be done if a teacher or school wants to and we can support you organizing the hub and sending snacks and gadgets where possible.
We strongly recommend you practice before the challenge. This year the competition is in the format of a Code Challenge together with some CTF challenges. You can train by trying the past training problems – for the CTF we recommend you to train with the problems of level 100. That way, you can better understand the type of challenge you might get and how to submit solutions. Plus, check the learning materials with a deep dive in the best approaches to solve both coding and CTF Challenges.
You can use any programming language to solve the problem.
Just visit the archive of the Code Challenge Teen Edition and the Cyber security challenge to find all the problem from past editions. Here you can upload as many solutions as you want, as many times as you want. The training problem submission works just like the real challenge, except you’ll play alone and not in a team.
Submit a solution by dragging and dropping it or uploading it from your computer. Each submission should contain at least one output file and at least one source code file. Note, the source file is not mandatory in sandbox mode.
Yes. You’ll see a list of scores for all your submissions.
No, but you’ll see your submission scores.
The platform supports the latest version of Chrome, Explorer, Firefox, Microsoft Edge and Safari. If you’re not sure what version you have, check here.
Try reloading the page, then try clearing your cache and cookies. If you’re still having problems, message the Reply Code Masters on chat or email challenges@reply.com.
You’ll need your own computer with an internet connection.
Just like most coding challenges, you can use your favourites. AI tools are allowed, check out the learn & train section to understand how AI can support you in the resolution of a problem.
On 12th March, at 3.30pm CET, we’ll publish the problem statement on the challenge platform. It will include the input files you can download from the challenge platform, where you’ll also submit your team’s solution files. The last input of each problem will be a CTF Challenge: just follow the instructions to submit the flag.
You can message the Reply Code Masters and Keen Minds in the Discord Server from your challenge page.
Yes. There are no restrictions on the development environment or programming language you use during the contest. You simply write programs to solve a task and submit the results as a text file to the challenge platform. You’re responsible for compiling and running your code on your own computer(s).
We’ll update the leaderboard regularly to show how teams are performing. We’ll also freeze it 30 minutes before the challenge deadline (but we’ll continue to update scores).
Yes, it’s an online-only coding competition.
The challenge consists of five algorithm-based problems. Each problem requires solving four different input files of increasing difficulty. The platform will automatically generate input files for each problem as soon as a player clicks on the button to generate the input. To help teams better understand each problem, we’ll publish the statement (detailing the problem to solve), some helpful assumptions, the input/output format, and some examples of correct input/output combinations.
Each problem has 4 input files. Together with the 4 input files, there will be one CTF challenge which, once solved, will double the points the team earn for that problem.
Teams have six hours to solve all the input files and the Capture the Flag challenges, from 15.30 CET to 21.30 CET.
Your team submits solutions through Reply’s challenge platform. Your team submits solutions for each input by uploading a text file to the challenge platform. A solution is made up of one output file for each input and source file. The uploaded source code is not executed during the challenge, but the Code Masters may inspect it at any time. The platform provides confirmation of output validation and the related score. Once you upload a submission, the input file will expire.
The Capture the Flag challenge requires a different format: you have to insert the string of the flag which is a token or a string that match the following regular expression: /\{FLG:.+\}/ where the content is any non-empty ASCII string (uppercase and lowercase letters, digits or symbols).
Teams can request an input as many times as needed until they provide the correct solution. Each new input is different from the previous one. For the last input of each problem and for the CTF points bonus, the platform won’t show the validation result in real-time. Instead, it will provide feedback only on how correct the format of your flag.
The platform will consider only your latest submission, even if it does not solve the problem, though you can request/submit as many inputs as you want.
We’ll calculate your team score by summing up the maximum score of each valid input file; the scoring system awards solutions that best optimise the problem. Reply Code Masters may, at any time, reject a solution and invalidate its score. To settle ties, we’ll take time into account.
Your team can use publicly released libraries and tools, but your solution must use original code. To be valid, every submission must include a file containing the source code of the program you developed to generate the output. Each source code file must be a UTF-8 plain text file or an archive of UTF-8 files.
If you result in the top teams in the podium, you are requested to provide also the write up file for the CTF challenge: a document which explain in detail how you and your team found the flag.
Yes, there are no restrictions on the type of development environment or programming language you can use.
During the competition, you write programs to solve a task and submit the results as a text file to the challenge platform. You’re responsible for compiling and running your code on your own computer(s).
Yes. You’ll see a list of scores for all your submissions.
The challenge platform has a regularly updated leaderboard, showing how teams are performing. It will freeze 30 minutes before the challenge ends.
Yes, you can use any of the AI tools you haver or you prefer.
We have a dedicated learning path with some concrete examples on how AI can support in the resolution of the problems for this challenge. Check the Learn & Train section to discover more and start practicing.
At the end of the game, the Reply Code Masters & Keen Minds will review and validate the best scoring submission from top-ranked teams on the leaderboard. The Reply Organizers’ decisions regarding the rules of the competition are final.
We’ll publish a full list of results and notify all finalists no later than 10 days after the day of the challenge.
Each member of the winning team will receive 1,500 euros. Each member of the second-ranked team will receive 800 euros, each of the third-ranked team will receive 500 euros.
Yes, you will get a certificate with the score and the ranking if your team send at least one valid submission.
If there’s a tie-break, we’ll consider the total resolution time for each input. In other words, the sum of completion times of all the solved input files. If two or more teams have the same score, the team with the shortest time wins.
By playing the Hack the Code Challenge Teen edition, you can win a prize for your High School, too. At the end of the Challenge, we’ll add your team’s final score to the High Schools Leaderboard.
Once the Challenge ends, the High School with the most points wins a €2,000 donation, plus a coding course designed for you by Reply experts. The more students you involve in the game, the more chance your school has to win the High School League.
To join the High Schools League, you must tell us the name of your school, right after you’ve created your team. On the day of the challenge, the points your team earns will contribute towards your school’s final score.
You’ll get some emails before and after the challenge, so check your mailbox regularly. You can always message the Reply Code Masters & Keen Minds during the challenge via chat if you have questions.
All communications will be in English. Though you and your teammates can speak whatever language(s) you like! 😊
Reply Code Masters and Keen Minds are gropus of Replyers passionate and experts about coding and security, developing this challenge in its versions: teen and standard. They write the problems and are responsible for enforcing all coding challenge rules. They’ll review submissions from teams and award prizes. They may exclude any participants or teams at any time, for breaching competition rules.
We want to make training sessions and the challenge fair for everyone. So never stop others from taking part – for instance, by overloading the challenge platform, or sending files containing malware, viruses or other code intended to interrupt, destroy or limit the operation of platform, software, hardware or telecoms equipment. This will result in instant disqualification. If you’ve spotted any cheating or unfair behaviour, email challenges@reply.com
Read the full Terms and Conditions about the competition