Code Arena pits two anonymous AI models against the same build request, generates working web apps in parallel sandboxes, and lets you inspect the code before voting for the better one.
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Code Arena is a browser-based evaluation environment on arena.ai where two anonymous AI models receive the same build request, generate working web applications in parallel sandboxes, and are judged by the person who asked. You prompt, wait for Option A and Option B to finish, open both previews, read the code each produced, and cast a preference vote that feeds the public Code Arena leaderboard.
This is not a coding assistant with one model behind it. Arena describes itself as an open platform to evaluate, benchmark, compare, and test frontier AI models, and Code Arena is that platform's coding surface — the votes are what power the leaderboards. Two generations share one interface: the original Code Arena, introduced in November 2025, produced front-end prototypes in a live preview, and Fullstack Code Arena, announced 2 July 2026, extended the same format to applications with a database, authentication, third-party API calls, and a deployment target.
A run follows a fixed sequence. An evaluator or developer submits a task such as "Build a markdown editor with dark mode." Models interpret the request and decide which actions to take using structured tool calls, then produce live, deployable web apps and sites, and every model action — file creation, edit, or execution — is logged and versioned. The resulting app is streamed through a secure frontend using CodeMirror 6 for source view and a live preview. That logging is the difference from a prompt playground: every generation includes a full project structure letting evaluators inspect how models manage interdependent files and recursive edits.
Battle Mode lets you compare two anonymous models in a head-to-head competition, and the model names are revealed immediately after you cast your vote. Code Arena adds a gate most comparison tools skip: in order for the voting options to appear you must preview both generations. Votes are aggregated through the Bradley-Terry rating system, originally developed for paired comparison experiments, and participation is uncapped.
Fullstack Code Arena gives the competing agents a database layer allowing them to generate code for PostgreSQL, user authentication, and Row Level Security. Agents can also safely connect to third party services and apps, such as calling an LLM, or connecting to a payments API, using a credential you supply — for instance bringing in an OpenAI key. Each build runs on a live dev server inside the sandbox with hot reloading, and agents can run any bash command as well as search the web for real-time information or documentation. Finished applications deploy directly to Vercel through a build-to-ship pipeline.
Full-stack mode is not a separate tab. You trigger it by structuring the prompt to indicate a full-stack application, either explicitly or by asking for a database, API, authentication, or backend functionality. When it is enabled the preview link is replaced with a / whose dropdown lists every page.
Every generation exposes a rendered site preview, the generated code blocks, a shareable preview link for peer testing or model comparison, and continued chat for iteration; full-stack builds add a database view and the page dropdown listing each route. Code sessions are restorable and persistent across visits, preserving state and enabling collaborative review.
Builds are assessed on three stated axes: functionality — does the app do what it's supposed to; usability — is it clear, responsive, and intuitive; and fidelity — does it match the requested design or behavior. Results do not collapse into one number. Since 26 February 2026 the WebDev leaderboard has been segmented into two categories reflecting different generation environments: HTML ranks standalone HTML/CSS/JS generation within a single document scope, while React ranks multi-file application generation including component structure, routing, state coordination, and cross-file consistency. A separate Fullstack leaderboard went live on 28 July 2026, covering multi-step reasoning, tool use, and end-to-end app generation.
New models do not sit unscored while votes accumulate. AutoEval uses a reward model in place of human votes, then follows the exact same Arena ranking methodology to compute the final arena score. Those entries are clearly labeled "AutoEval," then updated once enough human votes arrive to validate them, so a rank you read may be model-derived until the label disappears.
< > button.Enter. For a backend, name the components you want — database, API, authentication.Arena analysed more than 250,000 Code Arena prompts over five months and published the resulting taxonomy in May 2026. Users ask models to build multi-file React applications, implement dashboards, develop consumer products, create browser games, simulate dynamic systems, and build editing tools. Reference-Based Design is the most common category at roughly 29%, while Simulations account for about 15.3%. The vendor's own full-stack examples are narrower: an app with a sign up or login flow, like a members-only ecommerce app, and an app that stores a user's progress for them to come back to, like an education or learning app.
Bring the task you will assign a model rather than a demo prompt, then check whether the leaderboard filtered to the same technology and domain slice agrees with what you watched. For work that is not a build, Battle, Direct, and Side-by-Side handle isolated interactions, while Agent Mode at arena.ai/agent carries web search, image generation, file upload, coding assistance, and a sandbox/bash environment across a multi-step task.
Arena names three audiences for Fullstack Code Arena: entrepreneurs and small businesses, developers, and AI model labs. Those map onto different reasons to open the page.
Code Arena runs in the browser at arena.ai/code, inside the same interface as Arena's other modes. There is no desktop or mobile application in evidence, and the modality is a toggle — the < > button — rather than a separate site.
Signing in is not required, but an account changes what you get. You register with Google or with an email address that receives a verification link, and a signed-in account brings access to features that require user login, such as Direct mode, Side by Side mode, Image Arena, and Video Arena; higher rate limits compared to logged-out usage; and saved chat history that syncs across devices. Generated apps can call third-party services with an API key you provide, and a completed full-stack build deploys to Vercel, leaving Arena's sandbox for infrastructure you control.
Arena's Terms of Use, last updated 23 February 2026, state that the company currently offers the Service free of charge while retaining the right to charge for the Service, or any features or components thereof. Code Arena's Product Hunt launch on 13 February 2026 was framed the same way: prompt once, compare multiple AI-built apps for free. Free does not mean unmetered — separate throttles apply.
| Constraint | How it works | What lifts it |
|---|---|---|
| Daily usage balance | Credits usable however you want across Arena, replacing separate hidden limits across features and models | Automatic reset after 24 hours |
| Per-model rate limits | Each model has its own usage limits over time | Waiting for the reset |
| Overall chat rate limits | Limits on chat frequency regardless of model | Waiting for the reset |
| Feature access | Direct mode, Side by Side, Image Arena, Video Arena are gated | A free account |
The line that matters for planning is explicit: Arena does not offer a paid service that'll remove these rate limits, and if you hit one the only action available is to wait for it to reset. Arena also calls the daily limit one part of a rollout while it continues building the rest of the system.
Model Kombat by HackerRank runs coding LLMs head-to-head on real programming tasks where developers vote on which solution they'd actually ship, with language-specific leaderboards tracking which models lead in each programming language — closer if your work is backend rather than web UI. A directory listing of Arena competitors points elsewhere entirely: a playground for side-by-side LLM checks, an IDE that runs several coding agents at once, and platforms to build and evaluate multi-agent systems. Those are workspaces you control; Code Arena is a public evaluation venue, and the trade is privacy and configurability against a free, anonymised, leaderboard-connected comparison. An independent 2026 study comparing three vibe coding tools from a single generation prompt concluded that choosing between them involves structural trade-offs beyond perceived productivity.
The Code Arena page carries the warning that inputs are processed by third-party AI and responses may be inaccurate. It goes further: your conversations and certain other personal information will be disclosed to the relevant AI providers and may otherwise be disclosed publicly, and you are advised against submitting sensitive information that you would not want to be shared publicly. Conversations are also used for automated evaluation, with prompts sent to AI providers at a later time to score and compare their models, and an opt-out email route is published on the page.
The privacy policy, last updated 16 December 2025, sets the scope. User content data covers inputs, prompts, images, votes/ratings, and other content you upload or generate, plus associated metadata and interaction data such as whether you highlighted or copied a model's response. Arena may share and otherwise disclose that data with AI technology providers for their use in evaluating, improving, and developing their products and services, and may publish or otherwise make public data derived through the Service, including inputs and outputs.
The Terms confirm you are the owner of all right, title and interest in Your Content, but the company does not represent or warrant that the Outputs are protectible by any intellectual property rights. In parallel you grant Arena a perpetual, irrevocable, worldwide, royalty-free, sublicensable right to use, copy, reproduce, modify and adapt your content for all legal purposes. Access is limited solely to personal or internal business use, users must be at least 18 or the legal age to form a binding contract, and the Service is provided on an "as is" and "as available" basis, with all faults.
An independent benchmark tracker that republishes this coding data notes that applications which have mistakes or errors are still shown to the user, and that Arena infers from some statistics that models do sometimes produce errant output. A preference vote is not a correctness check. Independent 2025 research on the broader Arena method found that only 10% of poor-quality votes, from apathetic or adversarial annotators, can change model rankings by up to five places, and a separate 2025 study of roughly 2 million battles across 243 models argued that selective disclosure by providers biases arena scores. Both examine the human-preference method in general rather than Code Arena specifically, and Arena rejected the core allegation, stating that if a model provider chooses to submit more tests than another, this does not mean the second is treated unfairly. As of 8 September 2026 the WebDev overall leaderboard showed 663,027 votes across 127 models.
The Terms of Use state that Arena currently offers the Service free of charge while reserving the right to charge later. You can prompt without signing in, but an account raises your rate limits and saves chat history across devices.
No. Arena states that it does not offer a paid service that will remove these rate limits, and that the only action available when you hit one is to wait for it to reset. A separate daily balance of credits resets automatically after 24 hours.
Because you have not opened both builds — voting options appear only after you preview both generations.
Full-stack builds deploy directly to Vercel through the build-to-ship pipeline, and any build can be shared via a unique link. Legally you own your content, but Arena does not warrant that outputs are protectible by intellectual property rights.
Treat it as public. The page warns that conversations and certain other personal information will be disclosed to relevant AI providers and may otherwise be disclosed publicly, and the privacy policy says Arena may publish data derived through the Service.
Not on its own. The score aggregates human preference votes through the Bradley-Terry system, apps with mistakes are still shown to voters, and some entries are AutoEval-labelled estimates rather than accumulated human votes.