Creating and managing contests

The complete reference for contests on LCOJ: who can create them, where, what every field does, and what to do during and after a contest (ratings, MOSS, disqualification, data download).

⏱ ~30 min · 👤 Contest organizers, teachers · 🔑 judge.add_contest, judge.edit_own_contest (or judge.create_private_contest for organization contests)

Creating your first contest?

Follow the short First contest tutorial first, then come back here when you need to look up a specific field or feature.

Before you start

• Your account has the right permissions (see Who can create and edit contests).
• The problems you plan to use already exist and have been test-judged (see Managing problems).
• You have picked a scoring format (see Contest formats).
• For a class contest: the class organization exists and you are one of its admins.

Contest lifecycle

Stage	Condition	Who sees what
Draft	Publicly visible (is_visible) is off	Only authors, curators, testers and users with see_private_contest / edit_all_contest.
Published	is_visible on, before start_time	Allowed users (per access rules) see the contest page and can register (if enabled), but not the problems.
Running	start_time ≤ now ≤ end_time	Contestants click Join contest to start their timer.
Frozen	icpc/vnoj only, during the last frozen_last_minutes minutes	Contestants see the scoreboard as of the freeze. It stays frozen after the contest ends.
Ended	end_time < now	Anyone who can see the contest can read the problems and Virtual join.

Who can create and edit contests

Action	Required permission
Create a contest at /contests/new	judge.add_contest
Create an organization-private contest	Organization admin (or edit_all_organization) and judge.create_private_contest
Edit contests you author/curate (site or admin)	judge.edit_own_contest
Edit any contest	judge.edit_all_contest
Open the admin at /admin/judge/contest/	Staff account + edit_own_contest or edit_all_contest
Make a contest private / organization-private in the admin	judge.create_private_contest
Make any contest visible in the admin	judge.change_contest_visibility
Set an access code in the admin	judge.contest_access_code
Enable rating, click Rate	judge.contest_rating
Clone a contest	judge.clone_contest
Run MOSS	judge.moss_contest
Lock submissions (locked_after)	judge.lock_contest
Edit the problem label script	judge.contest_problem_label
Set a duration longer than VNOJ_CONTEST_DURATION_LIMIT	judge.long_contest_duration

For details and how to grant them, see Permissions.

Authors, curators and testers

• Authors (authors) and curators (curators) can edit the contest (with edit_own_contest). Curators are not listed as authors.
• Testers (testers) can see the contest and its problems before it starts, but cannot edit it.
• Authors, curators and testers cannot compete: when they join, they can only Spectate contest and are not ranked.

Where to create a contest

There are three places, which differ in how many fields they expose:

Place	Path	Use it for
Site create page	/contests/new (the Add new contest tab on /contests/)	Regular contests that only need the basic fields.
Organization page	/organization/<slug>/contest-create (the Create new contest tab in the organization)	Contests only for organization members.
Django admin	/admin/judge/contest/add/	Every field: registration, time limit, freeze, rating, pretests, and more.

The site create/edit form only has: key, name, start/end time, publicly visible, use clarifications instead of comments, hide tags, hide authors, show the settings summary, scoreboard visibility, format, description, access code, private and private contestants, plus the problem table (problem, points, order, max submissions). Staff users also see an Edit contest in admin panel for more options link on the edit page.

Option 1: Create on the site

1. Go to /contests/ and click the Add new contest tab.
2. Fill in Contest id, Contest name, Start time and End time.
3. Choose the Contest format and the display options.
4. In the Problems table, add each problem: pick it, enter its points, its order (a different number for each problem) and the Max submission count (blank for no limit). The Switch to drag and drop mode button lets you reorder by dragging.
5. Click Create. You automatically become an author of the contest.
6. For more options (time limit, freeze, rating, pretests…), open the contest in the admin.

Option 2: Organization-private contest

1. Open the organization page /organization/<slug> and click the Create new contest tab. The tab is only shown to organization admins who have create_private_contest.
2. The Contest id box is prefilled with the organization prefix; for example, the slug lop-10a1 gives the prefix lop10a1_. Keep the prefix and type the rest, for example lop10a1_quiz1.
3. Fill in the other fields as in Option 1. The Private contestants box only suggests organization members.
4. Click Create. The contest is automatically marked private to organizations and linked to this organization.
5. Turn on Publicly visible (on the form or later) so members can see the contest.

Key prefix rule

The prefix is the organization slug in lowercase with every non-alphanumeric character removed, followed by _. The edit page for an organization contest always checks this rule and shows Contest id must starts with <prefix> if the key is wrong. The create page currently does not check it, so if you delete the prefix while creating, later edits are blocked until you change the key.

Option 3: Django admin

1. Go to /admin/judge/contest/ and click Add.
2. Fill in the fields by group (see the sections below). Fields you lack permission for are shown read-only.
3. In the Problems block at the bottom, add problems and drag to reorder them.
4. Click Save. The admin does not add you as an author; pick authors in the Authors field.

Basic information

Field (admin)	English label	Meaning
key	Contest id	Unique, up to 32 characters, only a-z, 0-9, _. Used in the URL /contest/<key>.
name	Contest name	Up to 100 characters.
authors, curators, testers	Authors, Curators, Testers	See the box above.
description	Description	Markdown shown on the contest page.
terms	Terms	If set, contestants must tick I agree to the terms and conditions before joining or registering.
summary	Contest summary	Plain text for the meta description (social media previews).
og_image, logo_override_image	OpenGraph image, Logo override image	Share image, and a logo that replaces the site logo while users are in the contest. If empty, the organization's logo (if any) is used.
tags	Contest tags	Classification tags, created at /admin/judge/contesttag/.

Timing

Field	English label	Meaning
start_time	Start time	Contestants can join from this moment.
end_time	End time	Must be after start_time. Every live participation ends by this time.
time_limit	Time limit	(Admin only) Blank: everyone competes until end_time. Set (for example 03:00:00): each contestant gets exactly that much time from when they click join, but never past end_time.
registration_start, registration_end	Registration start time, Registration end time	(Admin only) If at least one is set, the contest requires registration: contestants click Register within this window. Once registration closes, only registered users can join. The window must start before start_time and end before end_time.

With time_limit, start_time–end_time becomes a window: contestants choose when to start inside it. Late starters get less time if the rest of the window is shorter than time_limit. Virtual contestants (joining after the contest ends) get time_limit, or the full contest length if none is set.

Mistranslated labels

In the Vietnamese admin, both registration_start and registration_end are labeled Thời gian tạo ("creation time"). The first is the registration start and the second is the registration end.

Duration limit

On the site create/edit form, a contest cannot last more than VNOJ_CONTEST_DURATION_LIMIT days (14 days on luyencode.net) unless you have long_contest_duration. The admin does not apply this limit. Note that contestants can keep practicing the problems after the contest ends, so a long duration is rarely needed.

Visibility and access

Field	English label	Meaning
is_visible	Publicly visible	Must be on for anyone outside the organizers to see the contest, including private and organization-private contests.
is_private	Private to specific users	Only users in private_contestants can see the contest.
private_contestants	Private contestants	The allowed users. You can paste a list of usernames into this box.
is_organization_private	Private to organizations	Only members of organization can see the contest.
organization	Organization	The organization that owns the contest.
access_code	Access code	If set, contestants must enter it when joining or registering (users who can edit the contest skip it).
view_contest_scoreboard	View contest scoreboard	These users can always see the full scoreboard, and can open the contest even if it is private.
banned_users	Personae non gratae	Barred from joining the contest (the Justice group in the admin).
disallow_virtual	Disallow virtual joining	Blocks Virtual join after the contest ends.
banned_judges	Banned judges	These judge servers will not grade the contest.

Who can open a contest that has is_visible on:

is_private	is_organization_private	Allowed users
Off	Off	Everyone, including anonymous visitors
Off	On	Organization members
On	Off	Users in private_contestants
On	On	Users who are organization members and in private_contestants

Organizers (authors, curators, testers), users in view_contest_scoreboard and users with see_private_contest or edit_all_contest can always open it.

Admin permissions

In the admin, users without create_private_contest cannot edit is_private, private_contestants, is_organization_private or organization; users with neither change_contest_visibility nor create_private_contest cannot edit is_visible. Users with only create_private_contest can only publish private or organization-private contests. The admin also has the bulk actions Mark contests as visible / Mark contests as hidden.

Scoreboard and display options

Field	English label	Meaning
scoreboard_visibility	Scoreboard visibility	See the table below.
ranking_access_code	Ranking access code	Unlocks the public ranking with a code.
show_submission_list	Show submission list	Lets contestants see others' submissions during the contest. After the contest, the list is always open (unless the scoreboard is frozen or hidden).
scoreboard_cache_timeout	Scoreboard cache timeout	Seconds to cache the scoreboard; 0 disables caching. Set a few seconds for large contests.
hide_problem_tags	Hide problem tags	Hide problem tags by default.
hide_problem_authors	Hide problem authors	Hide problem authors by default.
show_short_display	Show short form settings display	Show a rules summary on the contest page.
points_precision	Precision points	Decimal digits to round points to (0–10, default 3).
use_clarifications	No comments	Use the clarification system instead of comments (on by default). See During the contest.
push_announcements	Push announcements	Send a pop-up notification to contestants when there is a new announcement.

Scoreboard visibility options:

Value	English label	Behavior
V	Visible	The scoreboard is open throughout the contest.
C	Hidden for duration of contest	Hidden until the contest ends; during the contest, contestants only see their own row.
P	Hidden for duration of participation	Like C, but contestants whose own time has run out (for example with a time_limit) can see the full scoreboard before the contest ends. The Vietnamese label wrongly mentions virtual contests; this setting is about live participations.
H	Always hidden	Never public; only organizers and users in view_contest_scoreboard see it.

Format

The admin Format group holds Contest format, Frozen last minutes, Contest format configuration (JSON) and Contest problem label script. The site form only has Contest format. For choosing and configuring formats, see Contest formats.

Contest problems

Field	English label	On the site?	Meaning
problem	Problem	Yes	The problem. On the site you can only pick problems you can see.
points	Points	Yes	Maximum score for the problem in this contest (integer), independent of the problem's own points.
order	Order	Yes	Display order; each problem needs a different value.
max_submissions	Max submission	Yes	Maximum number of submissions; blank means unlimited.
partial	Partial	Admin only	Award partial points (on by default). Only effective if the problem itself allows partial points.
is_pretested	Is pretested	Admin only	The problem has pretests. Only effective when the contest has run_pretests_only on.
output_prefix_override	Output prefix length override	Admin only	How many characters of output contestants see in their results; overrides the problem setting.

Pretest judging:

1. In the admin, tick Is pretested for problems with pretests and turn on Run pretests only (run_pretests_only) in the Settings group.
2. During the contest, submissions are judged on pretests only.
3. After the contest, turn run_pretests_only off, save, then click Rejudge on each problem in the Problems block to judge on the full test set.

Rejudge and rescore

In the admin, each problem row has Rejudge (rejudge every contest submission for that problem) and Rescore (recompute points without rejudging). When you save a contest in the admin after changing the format, format configuration, freeze minutes or the problem table, LCOJ recomputes the whole scoreboard. The site edit page does not rescore; if you change points or the format on the site after submissions exist, use Rescore in the admin.

After the contest, users who can edit it see a Make All Problems Public button on the contest page: it makes every private problem in the contest public (you must be able to edit those problems) and publishes the editorials of problems you can edit.

Cloning a contest

The Clone tab on the contest page (requires clone_contest and edit access) makes a copy with a new key:

1. Enter the new key under Enter a new key for the cloned contest: and click Clone!.
2. The copy keeps the settings, problems and points, tags, organization, private contestants and view_contest_scoreboard; it is hidden, unlocked, and has you as its only author (curators and testers are not copied).
3. You are taken to its edit page to adjust the dates.

For organization contests, the new key must also follow the prefix rule.

Cloning on the site currently fails

The Clone tab (/contest/<key>/clone) currently shows a server error. For now, create a new contest and add the problems manually.

During the contest: announcements and clarifications

Announcements go to every contestant:

1. On the contest page, in the Announcements section, click Add an announcement (/contest/<key>/announce).
2. Enter the Announcement title and Announcement body (Markdown), then click Announce.
3. If the contest has Push announcements (push_announcements) on, every live contestant and spectator gets a pop-up notification right away (via Celery and WebSocket). Virtual contestants do not.

Announcements can also be added or edited in the admin (the announcement block at the bottom of the contest page); its Resend button sends one again.

Clarifications are attached to individual problems:

1. Open the problem in the admin (/admin/judge/problem/<id>/change/) and add a clarification with a Clarification body.
2. Clarifications appear in the Clarifications section of the contest page and on the problem page (when viewed in the contest). They do not send a pop-up notification; add an announcement if you need one.

With use_clarifications on, comments on the contest page are locked during the contest (and for anyone currently in it).

Official, public and frozen rankings

Kind	Path	Notes
Regular ranking	/contest/<key>/ranking/	Follows scoreboard_visibility. Has Show virtual participations, an organization filter and Download as CSV.
Public ranking	/contest/<key>/public_ranking/?code=<code>	Shows the full ranking to anyone with the ranking_access_code, ignoring scoreboard_visibility. Viewers still need access to the contest (private contests stay blocked).
Official ranking	/contest/<key>/official_ranking/	The Official Rankings tab, shown only when the Official ranking field (csv_ranking, Ranking group in the admin) has data: a CSV exported from CMS (columns Username, User, optional Team, per-problem columns, Global), or a URL starting with http to redirect to.

Freezing: only icpc and vnoj. During the last frozen_last_minutes minutes, contestants only see results from before the freeze; organizers still see the real scoreboard. It stays frozen after the contest. To reveal it, set frozen_last_minutes = 0 and save in the admin. See Scoreboard freeze.

Ranking replay and ghost participations

A contest is replayable when all of these hold: anonymous visitors can open it (public, not private), it has ended, frozen_last_minutes = 0, the scoreboard is visible, and the format is not ioi16. The ranking page then shows a time slider (⏱) to view the scoreboard at any moment, an End button to jump to the end and, for icpc/vnoj, a Freeze min box to try out freeze lengths. A virtual contestant in a replayable contest sees the scoreboard as of their own elapsed time (the Live button).

• Replay data is built on first view and stored as MEDIA_ROOT/contest_replay/<key>_v<version>.json; browsers cache it forever. On luyencode.net, DMOJ_CONTEST_REPLAY_INTERNAL is not set, so Django serves the file directly.
• If you rejudge or change results after the replay was built, open the contest in the admin and click Invalidate Replay (requires change_contest) to bump the version and rebuild it.
• Ghost participations: an operator can merge another contest's contestants (for example the original of a mirror) into the replay with the merge_replay_data command. The ranking page then gets a Show ghost participations checkbox.

After the contest

Rating

Ratings are not computed automatically. A user with contest_rating does this:

1. In the admin, make sure the Rating group has Contest rated (is_rated) on, and adjust:

   Field	English label	Meaning
   rate_all	Rate all	Also rate users who made no submissions.
   rate_disqualified	Rate disqualified	Also rate disqualified users (on by default; they rank last).
   rating_floor, rating_ceiling	Rating floor, Rating ceiling	Skip users whose current rating is below / above this.
   rate_exclude	Exclude from ratings	Exclude individual users (only participants can be picked).

2. After the contest ends, open it in the admin and click the Rate button in the bottom bar.

3. LCOJ deletes the ratings of this contest and every rated contest that ended after it, then recomputes them in end-time order. Only live participations (not virtual) are rated.

The Rate all ratable contests button on the admin contest list deletes all ratings and recomputes everything from scratch; use it only when you really need to.

MOSS plagiarism check

1. On the contest page, open the MOSS tab (/contest/<key>/moss). It appears if you can edit the contest and have moss_contest. MOSS needs a valid MOSS_API_KEY configured by the operator; without one, the tab still shows but running MOSS fails.
2. Click MOSS contest. LCOJ runs it in the background and shows a progress page.
3. The result is a problem × language table (C, C++, Java, Python, Pascal), each cell linking to the MOSS report. For each contestant, LCOJ sends their highest-scoring submission; a cell only has a result with at least 2 submissions.
4. Delete MOSS results clears old results; running again replaces them.

Operators can also run the runmoss command.

Disqualification and automatic bans

• On the ranking page, users who can edit the contest see a trash icon (Disqualify) next to each contestant; click and confirm to disqualify. Click the undo icon (Un-Disqualify) to reverse it. You can also do this in the admin at /admin/judge/contestparticipation/ (the Is disqualified box).
• A disqualified contestant's score becomes -9999 (ranked last), they are removed from the contest if they are in it, and they are added to the contest's Personae non gratae. If the contest already has ratings, they are recomputed immediately.
• Automatic ban: when VNOJ_SHOULD_BAN_FOR_CHEATING_IN_CONTESTS is on, a user disqualified in VNOJ_MAX_DISQUALIFICATIONS_BEFORE_BANNING or more contests that are not organization-private (starting on or after VNOJ_BAN_COUNT_FROM_DATE) gets their account banned. Un-disqualifying below the threshold lifts the ban (if the ban reason is exactly this message).

Setting	Default	luyencode.net
VNOJ_SHOULD_BAN_FOR_CHEATING_IN_CONTESTS	False	False: no automatic bans
VNOJ_MAX_DISQUALIFICATIONS_BEFORE_BANNING	3	3
VNOJ_BAN_COUNT_FROM_DATE	2026-01-01 (UTC)	2026-01-01
VNOJ_CONTEST_CHEATING_BAN_MESSAGE	Banned for multiple cheating offenses during contests	default

Locking submissions

The Contest lock field (locked_after, requires lock_contest) prevents the contest's submissions from being rejudged after that time. The bulk actions Lock contest submissions / Unlock contest submissions on the admin list lock them now or unlock them.

Downloading data

Contest authors can download every submission's source code as a ZIP file. See Contest data download.

Related site-wide settings

Operators set these in local_settings.py (see Environment and configuration):

Setting	luyencode.net	Effect
VNOJ_CONTEST_DURATION_LIMIT	14	Maximum duration (days) on the site form, unless the user has long_contest_duration.
MAX_CONTEST_PROBLEMS_COUNT	None	Maximum problems per contest (site form); None means unlimited.
VNOJ_OFFICIAL_CONTEST_MODE	False	Site-wide official contest mode: hides comments (except for superusers), blocks creating/editing blog posts, blocks editing the profile "about" and full name, stops contestants from aborting their own submissions, removes the join confirmation dialog, and logs the IP of every submission. Only enable it on a server dedicated to one official contest.
DMOJ_CONTEST_DATA_DOWNLOAD	True	Allows contest data downloads.
MOSS_API_KEY	from environment	MOSS key; must be valid for MOSS to run.

Verify

• The contest shows up at /contests/ when logged in as a contestant (or at /organization/<slug>/contests/ for organization contests).
• The contest page shows the right start/end time in your time zone.
• A tester account can open the problems before the start; an unauthorized account is refused.
• A test submission appears on the ranking with the correct score.
• After the contest: the scoreboard is unfrozen (if needed), Rate has been clicked (if rated) and MOSS has run (if needed).

Troubleshooting

Symptom	Cause and fix
Contestants cannot see the contest	Publicly visible is off; or the contest is private/organization-private and they are not in the list/organization.
Contest id must starts with …	An organization contest has the wrong key prefix. Change the key to use the reported prefix.
Contest duration cannot be longer than 14 days	Shorten the contest, edit it in the admin, or ask for long_contest_duration.
Problems must have distinct order.	Two problems share the same order. Give each a different number.
The Clone tab shows a server error	Cloning on the site currently fails; create a new contest and add the problems manually, see Cloning a contest.
No Rate button	Requires contest_rating; the contest must have is_rated on and must have ended.
No MOSS tab	Missing moss_contest, or no edit access.
Running MOSS fails	The server has no valid MOSS_API_KEY. Ask the operator to configure one.
The scoreboard is still frozen after the contest	Expected. Set frozen_last_minutes = 0 in the admin.
Points/format changed on the site but the scoreboard did not update	The site form does not rescore. Use Rescore in the admin or save the contest in the admin.
Replay shows old results after a rejudge	Click Invalidate Replay in the admin.
No replay slider	The contest is not replayable (private, frozen, hidden scoreboard, or ioi16 format).
Authors cannot compete	Expected: organizers can only Spectate contest. Use another account to test.
Clicking join shows Not registered with "You are not registered for this contest." (in Vietnamese, a wrong translation about edit permissions)	The contest requires registration, the user did not register, and registration has closed. Widen the registration window or leave both registration fields blank.

Next steps

• First contest: a step-by-step tutorial.
• Contest formats: scoring, penalties and freezing.
• Organizations (groups, classes): contests for a class.
• Contest data download.
• Permissions.