What it is
Technical challenges run on Piston, a code execution engine, with real runtimes for JavaScript, Python, and Java, versions 18.15, 3.10, and 15 respectively. Challenges can take the form of coding problems, debugging exercises, SQL queries, or written technical answers, and the system auto-detects the language being written in across a wider set that includes JavaScript, TypeScript, Python, Java, C++, Go, Rust, and C#.
Every coding challenge is checked against a mix of test cases the candidate can see and test cases kept hidden, the same structure used in real technical assessments, so passing the visible cases alone doesn't guarantee the submission is actually correct.
How it works
- 1
Pick a challenge
Choose a coding, debugging, SQL, or written technical problem, with a set difficulty level attached.
- 2
Write actual code
Work in a real editor rather than describing an approach out loud, with the system auto-detecting the language being written.
- 3
Run it against test cases
Submitted code executes for real through Piston's runtimes and gets checked against both visible and hidden test cases.
- 4
Use a hint if stuck
Hints are available on challenges that offer them, without needing to give up and restart.
- 5
Get pass/fail results, not a guess
Because the code actually runs, the result reflects whether the submission genuinely works, not an AI's read of whether it looks correct.
Real execution, not a code review
The difference between this feature and simply describing an approach to an AI is that the code here actually runs. A submission either passes the test cases or it doesn't, checked by execution rather than by a model reading the code and guessing whether it would work.
Hidden test cases matter
Visible test cases let a candidate check their own work as they go, but hidden test cases catch the edge cases a submission that only handles the obvious input would miss. That split mirrors how real technical assessments are usually built, rather than grading only on the cases already shown.
Detection covers more languages than execution does
The system can auto-detect code written in JavaScript, TypeScript, Python, Java, C++, Go, Rust, or C#, but the runtimes that actually execute submitted code cover JavaScript, Python, and Java specifically, through Piston. That distinction matters for a candidate deciding which language to write a solution in if getting a real pass/fail result matters.
Employers build their own challenges too
On the employer side, a custom technical challenge can be authored with an AI-drafted problem and answer key, then test-run before it's attached to a real job posting, which means the challenges candidates encounter through a job-board application can be specific to that employer's own hiring needs rather than a fixed generic bank.
Who it's for
Who it's for
Technical challenges suit candidates for roles where writing working code, querying a database, or debugging an existing problem is part of the actual hiring process, not just talking about how they'd approach it.
It's the hands-on counterpart to the technical interview type's spoken conversation, and it's also what employers use when they attach a custom coding assessment to a real job posting, which makes it worth practicing against the same mix of visible and hidden test cases a real assessment would use.
Frequently asked questions
Does submitted code actually run, or does an AI just read it?
It actually runs. Technical challenges use Piston, a real code execution engine, so a submission is checked by running it against test cases rather than by a model estimating whether the code looks correct.
Which languages can I actually get executed?
JavaScript, Python, and Java run for real through Piston's runtimes. The system can auto-detect a wider set of languages being written, including TypeScript, C++, Go, Rust, and C#, but real execution is limited to the three Piston covers.
What's the difference between a technical challenge and a technical interview?
A technical interview is a spoken conversation about reasoning, with no code involved. A technical challenge is a hands-on coding, debugging, SQL, or written problem with real code execution and test cases.
Are all the test cases visible before I submit?
No. Challenges use a mix of visible test cases a candidate can check against and hidden test cases that catch edge cases a narrow submission might miss.
Can employers create their own technical challenges?
Yes. Employers can author a custom challenge with an AI-drafted problem and answer key, test-run it, and attach it to their own job posting rather than relying only on a generic set.
Related pages
Write real code and get a real result
Take on a coding, debugging, SQL, or written technical challenge and get checked against actual test cases through real code execution, not a guess.