Agent skill

Rewardkit

by Arize-ai in Arize-ai/phoenix

Write Harbor task verifiers using Reward Kit. An agent skill from Arize-ai/phoenix.

Custom licenceAuto-check passedAI & LLM Engineering

Install Rewardkit

skills CLI
$ npx skills add Arize-ai/phoenix --skill rewardkit -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install Arize-ai/phoenix rewardkit --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/Arize-ai/phoenix.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/rewardkit .claude/skills/rewardkit && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
rewardkit
GitHub stars
12k
Token cost
~3k tokens
SKILL.md length
1,127 words
Files
1
Skills in repo
39
Repo updated
First seen
Licence
Custom licence

At a glance

Write Harbor task verifiers using Reward Kit. An agent skill from Arize-ai/phoenix.

  • Editing a tasks tests/ directory
  • SKILL.md covers Setup in a Harbor task, Programmatic criteria, Custom criteria and Judge criteria (LLM or…, plus 5 more sections
  • Calls uvx and uv; needs TYPESAFE_API_KEY and ANTHROPIC_API_KEY
  • Adding grading criteria

What it does

Rewardkit is an agent skill from Arize-ai/phoenix. Write Harbor task verifiers using Reward Kit. Use when creating or editing a task's tests/ directory, adding grading criteria, setting up LLM/agent judges, or designing verifiers that produce a reward score.

Its SKILL.md is about 3k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in AI & LLM Engineering. The repository describes itself as: AI Observability & Evaluation.

When your agent uses it

  • Editing a tasks tests/ directory
  • Adding grading criteria
  • Setting up LLM/agent judges
  • Designing verifiers that produce a reward score

Example prompts

  • “/rewardkit”

Requirements

  • Python 3
  • A credential in ANTHROPIC_API_KEY
  • A credential in TYPESAFE_API_KEY

What it can do on your machine

Read from SKILL.md and the folder at commit 52f76fc. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Shell commands in SKILL.md call:

    • uvx
    • uv

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md. Its commands use uvx and uv, which can reach the network depending on how they are called.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names these keys or tokens, usually read from environment variables:

    • TYPESAFE_API_KEY
    • ANTHROPIC_API_KEY

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Rewardkit loads about 3k tokens when it runs. Until then it costs about 54 tokens; SKILL.md has 1,127 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~54
When it runs · the whole SKILL.md, loaded when a task matches
~3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 1,127 words (~2,960 tokens).

“Help the user write task verifiers with Reward Kit. Reward Kit is a lightweight Python package that turns a directory of criteria files into a reward score. Each criterion is a Python function call or a TOML judge file; folders…”

— opening of SKILL.md by Arize-ai, Custom licence
name
rewardkit

Read the full SKILL.md on GitHub

Files

Just SKILL.md in .agents/skills/rewardkit of Arize-ai/phoenix.

Open the folder on GitHubat commit 52f76fc

Compare with similar skills

Rewardkit next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Rewardkit compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Rewardkit this skillArize-ai/phoenix12k—~3kAutomated safety check: PassCustom licence
Agent BuildershareAI-lab/learn-claude-code78k5 repos~1.2kAutomated safety check: PassMIT
Add Uint Supportpytorch/pytorch104k2 repos~2.3kAutomated safety check: PassCustom licence
LLM Benchmarking with lm-evaluation-harnessOrchestra-Research/AI-Research-SKILLs13k8 repos~3kAutomated safety check: PassMIT
Segment Anything Model GuideOrchestra-Research/AI-Research-SKILLs13k8 repos~3.3kAutomated safety check: PassMIT
1passwordtrpc-group/trpc-agent-go1.9k14 repos~656Automated safety check: PassApache-2.0

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Questions about Rewardkit

What does Rewardkit do?

Write Harbor task verifiers using Reward Kit. An agent skill from Arize-ai/phoenix. Rewardkit is an agent skill from Arize-ai/phoenix. Write Harbor task verifiers using Reward Kit.

When should I use Rewardkit?

Rewardkit fits situations like: editing a tasks tests/ directory; adding grading criteria; setting up LLM/agent judges; designing verifiers that produce a reward score.

How do I install Rewardkit in Claude Code?

Run `npx skills add Arize-ai/phoenix --skill rewardkit -a claude-code`. Or copy the skill folder (.agents/skills/rewardkit in Arize-ai/phoenix) into .claude/skills/rewardkit in your project. Claude Code loads it when a task matches its description.

How do I install Rewardkit in Codex?

Run `npx skills add Arize-ai/phoenix --skill rewardkit -a codex`. Or copy the skill folder (.agents/skills/rewardkit in Arize-ai/phoenix) into .agents/skills/rewardkit in your project. Codex loads it when a task matches its description.

Can I use Rewardkit in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add Arize-ai/phoenix --skill rewardkit -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/rewardkit, .gemini/skills/rewardkit, .github/skills/rewardkit and .opencode/skills/rewardkit in your project.

What does Rewardkit need to run?

Going by SKILL.md and its folder, Rewardkit needs the command-line tools its instructions call (uvx and uv) and credentials named TYPESAFE_API_KEY and ANTHROPIC_API_KEY. Our summary lists: Python 3; A credential in ANTHROPIC_API_KEY; A credential in TYPESAFE_API_KEY.

Does Rewardkit access the network?

SKILL.md contains no URLs. Its commands use uvx and uv, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Rewardkit safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Rewardkit use?

Rewardkit has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does Rewardkit use?

About 3k tokens (SKILL.md is roughly 12k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Rewardkit?

Skills that share tags, products or a category with Rewardkit: Agent Builder (shareAI-lab/learn-claude-code, 78k stars), Add Uint Support (pytorch/pytorch, 104k stars), LLM Benchmarking with lm-evaluation-harness (Orchestra-Research/AI-Research-SKILLs, 13k stars) and Segment Anything Model Guide (Orchestra-Research/AI-Research-SKILLs, 13k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Rewardkit?

Arize-ai (a GitHub organization) maintains it in Arize-ai/phoenix, which has 11,764 GitHub stars. The repository holds 39 skills in this directory. The repository was last updated on October 9, 2026.

Source: Arize-ai/phoenix on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.