Need help with judge-server?
Click the “chat” button below for chat support from the developer who created it, or find similar developers for support.

About the developer

656 Stars 155 Forks GNU Affero General Public License v3.0 3.6K Commits 43 Opened issues


Judging backend server for the DMOJ online judge.

Services available


Need anything else?

Contributors list

DMOJ Judge amd64 Build Status arm64 Build Status FreeBSD Build Status Coverage Slack

Python AGPLv3 contest judge backend for the DMOJ site interface. See it in action at!

A modern online judge and contest platform system, supporting IO-based, interactive, and signature-graded tasks, with runtime data generators and custom output validators.

Supported Platforms and Runtimes

The judge implements secure grading on Linux and FreeBSD machines.

| | Linux | FreeBSD | |------ |------- |--------- | | x64 | | | | x86 | ✔ | ¯\_(ツ)_/¯ | | x32 | ✔ | — | | ARM | ✔ | ❌ |

Versions up to and including v1.4.0 also supported grading on Windows machines.

The DMOJ judge does not need a root user to run on Linux machines: it will run just fine under a normal user.

Supported languages include: * C++ 11/14/17/20 (GCC and Clang) * C 99/11 * Java 8/9/10/11/15 * Python 2/3 * PyPy 2/3 * Pascal * Perl * Mono C#/F#/VB

The judge can also grade in the languages listed below. These languages are less tested and more likely to be buggy. * Ada * AWK * COBOL * D * Dart * Fortran * Forth * Go * Groovy * Haskell * INTERCAL * Kotlin * Lua * NASM * Objective-C * OCaml * PHP * Pike * Prolog * Racket * Ruby * Rust * Scala * Chicken Scheme * sed * Steel Bank Common Lisp * Swift * Tcl * Turing * V8 JavaScript * Brain**** * Zig


Installing the DMOJ judge creates two executables in your Python's script directory:

is used to connect a judge to a DMOJ site instance, while
provides a command-line interface to a local judge, useful for testing problems.

For more detailed steps, read the installation instructions.

Note that the only officially-supported Linux distribution is the latest Debian, with the default

versions of all runtimes. This is what we run on, and it should "just work". While the judge will likely still work with other distributions and runtime versions, some runtimes might fail to initialize. In these cases, please file an issue.

Stable Build

PyPI version PyPI

We periodically publish builds on PyPI. This is the easiest way to get started, but may not contain all the latest features and improvements.

$ pip install dmoj

Bleeding-Edge Build

This is the version of the codebase we run live on

$ git clone --recursive
$ cd judge-server
$ pip install -e .

Several environment variables can be specified to control the compilation of the sandbox:

    ; set it to
    if you're building on a pre-Linux 3.5 kernel to disable
    filtering in favour of pure
    (slower). This flag has no effect when building outside of Linux.
    ; use it to override the default architecture specified for compiling the sandbox (via
    ). Usually this is
    , but will not be specified on ARM unless
    is set (a generic, slow build will be compiled instead).

With Docker

We maintain Docker images with all runtimes we support in the runtimes-docker project.

Runtimes are split into three tiers of decreasing support. Tier 1 includes Python 2/3, C/C++ (GCC only), Java 8, and Pascal. Tier 3 contains all the runtimes we run on Tier 2 contains some in-between mix; read the

for each tier for details. These images are rebuilt and tested every week to contain the latest runtime versions.

The script below spawns a tier 1 judge image. It expects the relevant environment variables to be set, the network device to be

, problems to be placed under
, and judge-specific configuration to be in
. Note that runtime configuration is already done for you, and will be merged automatically into the
$ git clone --recursive
$ cd judge-server/.docker
$ make judge-tier1
$ exec docker run \
    --name judge \
    -p "$(ip addr show dev enp1s0 | perl -ne '[email protected] (.*)/.*@ and print$1 and exit')":9998:9998 \
    -v /mnt/problems:/problems \
    --cap-add=SYS_PTRACE \
    -d \
    --restart=always \
    dmoj/judge-tier1:latest \
    run -p15001 -s -c /problems/judge.yml \


Running a Judge Server

$ dmoj --help
usage: dmoj [-h] [-p SERVER_PORT] -c CONFIG [-l LOG_FILE] [--no-watchdog]
            [-a API_PORT] [-A API_HOST] [-s] [-k] [-T TRUSTED_CERTIFICATES]
            [-e ONLY_EXECUTORS | -x EXCLUDE_EXECUTORS] [--no-ansi]
            server_host [judge_name] [judge_key]

Spawns a judge for a submission server.

positional arguments: server_host host to connect for the server judge_name judge name (overrides configuration) judge_key judge key (overrides configuration)

optional arguments: -h, --help show this help message and exit -p SERVER_PORT, --server-port SERVER_PORT port to connect for the server -c CONFIG, --config CONFIG file to load judge configurations from -l LOG_FILE, --log-file LOG_FILE log file to use --no-watchdog disable use of watchdog on problem directories -a API_PORT, --api-port API_PORT port to listen for the judge API (do not expose to public, security is left as an exercise for the reverse proxy) -A API_HOST, --api-host API_HOST IPv4 address to listen for judge API -s, --secure connect to server via TLS -k, --no-certificate-check do not check TLS certificate -T TRUSTED_CERTIFICATES, --trusted-certificates TRUSTED_CERTIFICATES use trusted certificate file instead of system -e ONLY_EXECUTORS, --only-executors ONLY_EXECUTORS only listed executors will be loaded (comma-separated) -x EXCLUDE_EXECUTORS, --exclude-executors EXCLUDE_EXECUTORS prevent listed executors from loading (comma- separated) --no-ansi disable ANSI output --skip-self-test skip executor self-tests

Running a CLI Judge

$ dmoj-cli --help
usage: dmoj-cli [-h] -c CONFIG
                [-e ONLY_EXECUTORS | -x EXCLUDE_EXECUTORS]

Spawns a judge for a submission server.

optional arguments: -h, --help show this help message and exit -c CONFIG, --config CONFIG file to load judge configurations from -e ONLY_EXECUTORS, --only-executors ONLY_EXECUTORS only listed executors will be loaded (comma-separated) -x EXCLUDE_EXECUTORS, --exclude-executors EXCLUDE_EXECUTORS prevent listed executors from loading (comma- separated) --no-ansi disable ANSI output --skip-self-test skip executor self-tests


For info on the problem file format and more, read the documentation.

We use cookies. If you continue to browse the site, you agree to the use of cookies. For more information on our use of cookies please see our Privacy Policy.