Judge0 open-source online code execution API system

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Judge0 is a free and open-source online code execution tool that securely runs code in over 90 programming languages. It operates efficiently, supports elastic scaling, and adopts a sandbox isolation mechanism, making it suitable for scenarios such as AI agents, programming platforms, online education, and job technical assessments. You can easily execute code through its simple API or Python SDK – either by hosting it yourself or directly using cloud services. With Judge0, you can quickly build applications without having to manage servers, saving development time and ensuring the security of your code tests.

When building online programming platforms, code evaluation systems, or teaching tools, a core question persists:

How do I securely run user-submitted code on my server?

Judge0 offers exactly this capability

It is an open-source online code execution and evaluation system that provides a complete process of “code commit, →compilation, running, → returning results” through standardized APIs.

Project positioning

At its core, Judge0 is not a graphical software, but:

A RESTful code execution API service

It allows external systems to submit source code via HTTP requests, specify the language and running parameters, and then obtain the execution results, including:

  • Standard output (stdout)
  • Standard Error (stderr)
  • Runtime
  • Memory Usage
  • Exit status code

This allows it to be integrated into various platforms as a back-end foundational component.

Supported languages and operating environments

Judge0 supports more than 90 languages and runtime configurations, including but not limited to:

  • C / C++
  • Python
  • Java
  • Go
  • Rust
  • JavaScript
  • Kotlin
  • Swift

It should be noted that the number of languages includes different versions and running environments, so “90+” is more accurately understood as a combination of multiple languages and multiple running configurations.

Security mechanism and enforcement method

Judge0 executes code through container isolation (usually based on Docker and isolate).

Each code commit runs in a controlled environment and can be set to:

  • Time Limit
  • Memory Limit
  • CPU limits

This sandbox mechanism prevents malicious code from affecting the host system and is a key capability of online evaluation systems.

How to use:

Judge0 is API-first designed.

The typical process is as follows:

  1. Submit Code (POST Request)
  2. Get the commit ID
  3. Query execution results (polling or callbacks)

Example request structure:

{
 "source_code": "print('hello')",
 "language_id": 71
}

Back example:

{
 "stdout": "hellon",
 "time": "0.01",
 "memory": 12345
}

Since it’s a standard REST API, it can be called in any language (Python, Node.js, PHP, Go, etc.).

Deployment method

Judge0 offers several deployment options:

  • Docker Compose deployment
  • Containerized operation
  • Kubernetes cluster deployment
  • Use the official public API instance

If you deploy it yourself, you need a server environment; If you use public APIs, you can eliminate infrastructure management.

Application scenarios

Common applications for Judge0 include:

  • Online Evaluation System (OJ)
  • Programming practice platform
  • Teaching automatic correction system
  • The code of the online IDE runs the backend
  • Technical evaluation system
  • Code sandbox service

In recent applications, it can also be used as an execution engine for AI-generated code, but this use is an extension scenario rather than the original positioning of the project.

Technical characteristics:

  • Open Source (MIT License)
  • Multilingual support
  • Sandbox isolation enforcement
  • API-driven design
  • Scalable queue mechanism
  • Support asynchronous task processing

Judge0 is more of an “infrastructure component” than an end-user-facing application.

Github：https://github.com/judge0/judge0
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