arena is a skill in Jakeschincariol/arena-skill, last changed 26 Sept 2026. It can run shell commands and bundle scripts.
Make 100 versions of Claude fight to the death over one task. Spins up N sub-agents (default 100, --quick for 16), gives every one the exact same task plus a different strategy card (reasoning mode, workflow, strategy), then runs a single-elimination bracket: they attack each other's solutions, defend and revise, and a judge scores every match on a written rubric until one solution survives. Use when the user is not satisfied with an answer, calls it a bad answer, says try again or do better, says "arena", or asks to make them compete.
At a glance
What it can touch
How much a skill can do, not whether it is risky.
Pattern check
Nothing flagged
That isn't proof the skill is harmless.
Commit df07b8e · 1 Nov 2026
How the check worksPattern check: nothing flagged
That isn't proof the skill is harmless.
Install
Each tab says whether it installs commit df07b8e, the one we checked, or the latest version.
OpenCode also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Goose also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Windsurf (Devin Desktop) also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Zed also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Roo Code also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Factory Droid also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Junie also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
Amp also looks in .agents/skills/ and ~/.agents/skills/, so use the Any agent steps.
No install command here reaches Kiro. Copy the skill's folder into .kiro/skills/ in your project, or ~/.kiro/skills/ for all your projects. Jakeschincariol/arena-skill/skills/arena (opens in a new tab)
Antigravity also looks in .agents/skills/, so the Any agent steps reach it with This project. For All projects, see where Antigravity looks.
Cline also looks in .claude/skills/, so the Claude Code steps reach it with This project. For All projects, see where Cline looks.
Claude Code
Pinned to commit df07b8e, the one we checked.
From your project's root folder:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&mkdir -p .claude/skills &&mkdir .claude/skills/arena &&cp -R "$tmp"/skills/arena/. .claude/skills/arena/ &&rm -rf "$tmp"If Claude Code was already running and this created the skills folder, run /reload-skills.
Or install the arena-skill plugin it ships in. Installs the latest version, not the one we checked. Installs everything in the plugin, including any hooks, MCP servers and scripts our check doesn't cover.
claude plugin marketplace add Jakeschincariol/arena-skill --scope project &&claude plugin install arena-skill@arena-skill --scope projectClaude apps
Pinned to commit df07b8e, the one we checked.
Skills in the Claude apps belong to your account rather than to a project.
Make arena.zip, with the skill folder at the top level:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&out="$(mktemp -d)" &&cp -R "$tmp"/skills/arena "$out"/arena &&(cd "$out" && zip -qr - arena) > arena.zip &&rm -rf "$tmp" "$out"In Claude, open Customize > Skills, select +, then + Create skill > Upload a skill, and choose arena.zip.
On Free, Pro and Max plans, turn on Code execution and file creation (Create and edit files in newer settings) under Settings > Capabilities.
Codex
Pinned to commit df07b8e, the one we checked.
From your project's root folder:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&mkdir -p .agents/skills &&mkdir .agents/skills/arena &&cp -R "$tmp"/skills/arena/. .agents/skills/arena/ &&rm -rf "$tmp"Codex picks up new skills on its own; restart it if this one does not appear.
Cursor
Pinned to commit df07b8e, the one we checked.
From your project's root folder:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&mkdir -p .cursor/skills &&mkdir .cursor/skills/arena &&cp -R "$tmp"/skills/arena/. .cursor/skills/arena/ &&rm -rf "$tmp"Copilot & VS Code
Pinned to commit df07b8e, the one we checked.
From your project's root folder:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&mkdir -p .github/skills &&mkdir .github/skills/arena &&cp -R "$tmp"/skills/arena/. .github/skills/arena/ &&rm -rf "$tmp"In a running Copilot CLI session, run /skills reload.
Or install it with gh skill, which also installs the commit we checked. Needs GitHub CLI 2.90 or later.
gh skill install Jakeschincariol/arena-skill skills/arena/SKILL.md@df07b8e518e10cdecd8cd7712d9958b6f396250e --agent github-copilot --scope projectGemini CLI
Pinned to commit df07b8e, the one we checked.
From your project's root folder:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&mkdir -p .gemini/skills &&mkdir .gemini/skills/arena &&cp -R "$tmp"/skills/arena/. .gemini/skills/arena/ &&rm -rf "$tmp"In a running session, run /skills reload.
Or use Gemini CLI’s own installer. Installs the latest version, not the one we checked.
gemini skills install https://github.com/Jakeschincariol/arena-skill.git --path skills/arena --scope workspaceAny agent
Pinned to commit df07b8e, the one we checked.
OpenCode, Goose, Windsurf (Devin Desktop), Zed, Roo Code, Factory Droid, Junie, Amp and Antigravity read .agents/skills in a project.
From your project's root folder:
tmp="$(mktemp -d)" &&git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/Jakeschincariol/arena-skill.git "$tmp" &&git -C "$tmp" fetch -q --depth 1 origin df07b8e518e10cdecd8cd7712d9958b6f396250e &&git -C "$tmp" sparse-checkout set -- skills/arena &&git -C "$tmp" checkout -q df07b8e518e10cdecd8cd7712d9958b6f396250e &&mkdir -p .agents/skills &&mkdir .agents/skills/arena &&cp -R "$tmp"/skills/arena/. .agents/skills/arena/ &&rm -rf "$tmp"Or use the skills CLI from skills.sh. Installs the latest version, not the one we checked. The skills CLI reports installs to skills.sh unless you set DISABLE_TELEMETRY=1.
npx skills@1.7.4 add Jakeschincariol/arena-skill --skill arenaWhat it can touch
From the files and frontmatter at commit df07b8e. This is how much a skill can do, not whether it is risky.
Pattern check
Pattern check: nothing flagged · commit df07b8e · 1 Nov 2026
We checked every text file in this skill, at commit df07b8e on 1 Nov 2026, against 45 published patterns such as download-and-run commands, hidden text and credential access. We don't run the skill, we don't read the web pages it points to, and we can't judge everything its instructions might lead an agent to do. In published tests, pattern checks like this one missed most malicious skills. Read the skill before you install it — especially anything it asks you to download or run.
Format check
Each agent reads SKILL.md a little differently. We check the file against each one's published rules; we don't run the skill in any agent.
Agent Skills specPasses with warnings
The open format from agentskills.io, held to what the strictest agents enforce, so one folder loads everywhere.
- Warning
Fields outside the spec: argument-hint (read by Claude Code and VS Code). Uploads to the Claude apps and API, and the spec's validator, reject the file; most agents ignore these fields. O1
Fix: Delete them for a portable skill, or keep them if you only target the agents that read them.
- Note
There is no license field, so readers can't tell whether they may reuse the skill. O2
Fix: Add license: with an SPDX name such as MIT or Apache-2.0, or the name of a bundled licence file.
- Note
Reference files that SKILL.md doesn't link: rubric.md. Anthropic suggests linking every reference file directly from SKILL.md. B4
Fix: Link each one from SKILL.md and say when to read it.
- Warning
Claude CodePasses
Claude Code reads its own extra fields, ignores unknown ones, and still loads a skill whose frontmatter is broken, without its fields.
- Note
Reference files that SKILL.md doesn't link: rubric.md. Anthropic suggests linking every reference file directly from SKILL.md. B4
Fix: Link each one from SKILL.md and say when to read it.
- Note
Claude apps & API uploadFails
Uploading to claude.ai or the Claude API, or packaging with Anthropic's script, accepts only the six spec fields and stops on anything else.
- Error
Upload and packaging fail on fields outside the spec: argument-hint. O1
Fix: Delete them, and keep your own data under metadata as text values.
- Note
The description is 541 characters. The claude.ai Help Center says 200 at most, though Anthropic's API docs and validator allow 1,024. D4
Fix: If the claude.ai upload refuses it, trim the description to 200 characters.
- Note
Reference files that SKILL.md doesn't link: rubric.md. Anthropic suggests linking every reference file directly from SKILL.md. B4
Fix: Link each one from SKILL.md and say when to read it.
- Error
OpenAI (Codex & API)Passes with warnings
Codex finds SKILL.md by its exact name and needs a description; OpenAI's Skills API checks the frontmatter against the spec and caps uploads.
- Warning
Fields outside the spec: argument-hint. Codex ignores them; OpenAI doesn't say whether its upload accepts them. O1
Fix: Delete them, or move your own data under metadata as text values.
- Warning
- VS Code & CopilotPasses
SKILL.md
Files
4 files
| Path | Size |
|---|---|
| SKILL.md (opens in a new tab) | 18.6 KB |
| bracket.py (opens in a new tab) | 48.3 KB |
| rubric.md (opens in a new tab) | 3.6 KB |
| strategies.json (opens in a new tab) | 9 KB |
Other Agent tooling skills
Same category, most repo stars first.