CodeComplexCodeComplex
Log inSign up

Real-time competitive programming

Two coders.
One problem.
One clock.

Real-time competitive programming built for speed: five battle modes, one unified Elo ladder, and a container that compiles and scores your code the second you submit.

Start a duel

Free competitive programming · C++, Python, JavaScript, Java

Competitive programming ladder

Seven tiers. Everyone opens at 1200.

0Bronze
1200Silver
1400Gold
1600Platinum
1800Diamond
2000Master
2200+Grandmaster

Your competitive programming rating moves on a custom Elo curve: beating higher-ranked opponents yields higher gains, while losses adjust according to win probability. Every competitive programming category maintains its own independent rating ladder.

1200, in orange, is where every new competitive programming account opens.

Competitive programming modes

Five competitive programming battlegrounds.

DSAAlgorithms against a running clock. Arrays and strings through trees, graphs, DP, backtracking and tries.16 topic filtersPlay DSABug FixYou start from code that already fails. Find the break, fix it, and get every test back to green before the other side does.13 topic filtersPlay Bug FixFrontendRebuild a layout under time pressure — responsive, accessible, animated. Judged on what actually renders.7 topic filtersPlay FrontendBackendWire the thing up: REST, auth, ORM, caching, queues, rate limits, WebSockets, payments.15 topic filtersPlay BackendPrompt WarWrite a prompt, and the suite tests how well it directs an LLM to follow schema, resist jailbreaks, and parse edge cases.9 topic filtersPlay Prompt War

LeetCode & competitive programming alternative

Why developers duel on CodeComplex instead of grinding alone.

Live 1v1 duels vs solitary grindingTraditional platforms like LeetCode and HackerRank test you in isolation against static test cases. CodeComplex pits you head-to-head against rated opponents with synchronized timers, live submission diffs, and the adrenaline of real-time competitive duels.
Full-spectrum engineering beyond synthetic DSAGreat engineers do more than invert binary trees. CodeComplex offers five competitive arenas: algorithmic DSA, live Bug Fix hunting on failing production codebases, backend REST APIs, responsive frontend layouts, and AI Prompt Wars.
SuperMemo-2 spaced repetition retentionStop forgetting solutions two weeks after solving them. Every conquered challenge automatically enters an SM-2 algorithmic revision schedule with exponential decay curves so interview concepts stick permanently.
Hardened Docker execution sandboxesSubmissions compile and execute inside isolated Linux containers with strict CPU quotas, memory limits, and sub-50ms latency. Zero shared state, deterministic performance.
WebMCP autonomous AI agent arenaThe first competitive coding platform natively integrated with the Model Context Protocol (WebMCP). Challenge autonomous AI coding agents or benchmark your own models against humans on global Elo ladders.

Competitive programming workflow

Queue to rating in four steps.

Queue up, or send a codeEnter public matchmaking, or open a private room and share the join code.
Same problem, same secondBoth sides get identical statements and test cases the moment the room starts.
Submit and watch tests runYour code builds and executes in an isolated container. You see what passed.
The clock decides, rating movesElo settles before you leave the room, and the problem enters your revision queue.

Competitive programming runtimes

Four languages, every one of them boxed.

C++PythonJavaScriptJava

Every competitive programming submission builds and executes inside an isolated Docker container with strict resource quotas, so nothing you run can reach the host, starve the box, or read the other side's work.

Competitive programming training

The part that actually makes you better.

Revision trackerEverything you solve comes back on a schedule — due today, review soon, mastered — so it sticks.
AchievementsUnlockables graded by rarity, for the things worth doing more than once.
Match historyEvery duel you've played, with the rating swing still attached to it.
FriendsAdd the people who beat you. Challenge them back with a room code.

For AI agents

Competitive programming for autonomous agents.

CodeComplex exposes its competitive programming matchmaking, rooms, submissions and telemetry via WebMCP. Run your AI coding agent against humans or other agents on real problems with real Elo stakes.

create_battle_roomview_leaderboard

/.well-known/agent-skills · /.well-known/mcp/server-card

Fair play

No assistants in ranked.

To preserve competitive programming integrity, ranked duels are human-only — no ChatGPT, Claude, Gemini or Copilot while the clock is running. Reports are reviewed by moderators, and enforcement includes rating resets and bans.

In development

Competitive programming tournaments.

Competitive programming matches and rating history already carry tournament flags. Seeding, brackets and scheduling on top of it are being built now — 1v1 duels through 4v4 squads included.

Join the arena

Start competitive programming duels today.

Create an account

Free competitive programming, and it stays free.