CodeBattle

Two developers. One problem. One winner.

A private coding duel for you and a friend. Share a link, solve the same challenge against the clock, and let the judge pick the winner — not your stopwatch.

How a match works

ProblemEasy · Arrays

Two Sum

Return indices of the two numbers that add up to target. Exactly one solution. Same element twice is illegal.

nums = [2, 7, 11, 15]

target = 9 → [0, 1]

You● typing

1function twoSum(nums, target) {2  const seen = new Map();3  for (let i = 0; i < nums.length; i++) {4    const need = target - nums[i];5    if (seen.has(need)) return [seen.get(need), i];6    seen.set(nums[i], i);7  }8}

Opponentread-only

1function twoSum(nums, target) {2  for (let i = 0; i < nums.length; i++) {3    for (let j = i + 1; j < nums.length; j++) {4      if (nums[i] + nums[j] === target) {5        return [i, j];6      }7    }8  }9}

GitHub
OAuth sign-in — no passwords
A friend
Share one invite link
JavaScript
Only language in V1
15 min
Default clock per duel

How a match works

From invite link to rating change in four steps.

Built for a real duel with someone you know — not a random queue, not a spectator sport.

01
Create a private room
Pick a difficulty, get a shareable link. No matchmaking queue — you choose who you face.
02
Both ready, then the clock
When both players ready up, the server starts the timer. Your clocks are not trusted.
03
Code under pressure
Same problem, separate editors. You can see that they are typing — not their full solution.
04
First accepted submission wins
Hidden tests decide it. Rating moves when the judge accepts a solution.

Why it feels fair

The browser is just the arena. The server keeps score.

CodeBattle is for people who want a clean head-to-head: same prompt, same language, same deadline, honest result. Cheat the UI and you still lose to the judge.

Server decides the winner
Finish time, acceptance, and ELO live on the API — not in the browser.
Invite-only 1v1
No public lobby spam. One link, two seats, one problem.
JavaScript on the clock
V1 is JS-only so the match stays fair and the judge stays simple.

Two developers. One problem. One winner.

From invite link to rating change in four steps.

Create a private room

Both ready, then the clock

Code under pressure

First accepted submission wins

The browser is just the arena. The server keeps score.

Server decides the winner

Invite-only 1v1

JavaScript on the clock