# promptfoo-evaluation

A skill that walks the agent through setting up Promptfoo evaluations: promptfooconfig.yaml, Python assertions, and LLM-as-judge rubrics.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1500 installs · ★ 1493
- Author: daymade
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/daymade/claude-code-skills/tree/HEAD/promptfoo-evaluation/SKILL.md
- Updated: 2026-10-25
- HTML: https://affpapa.org/en/nevibecode/skills/promptfoo-evaluation

## What it does

The skill covers the usual Promptfoo layout: one main config, a `prompts/` folder with markdown and chat-format JSON prompts, `tests/cases.yaml` for test cases, and `scripts/` for custom Python checks. Runs go through `npx promptfoo@latest init`, then `eval`, and `view` opens the results in a browser.

Assertions range from built-in `contains`, `equals`, `regex` and `latency` to your own Python function. That function receives the output and a context dict and returns `pass`, `score` and a reason. For subjective quality there is `llm-rubric`, where a grader model scores against criteria you write and a `threshold` you set.

Two things bite people. First, if you call models through a relay or proxy, every `llm-rubric` needs its own `provider` block with `apiBaseUrl` — the main provider's setting is not inherited, so the grader hits the default endpoint and comes back with a 401. Second, `file://` paths resolve from the location of `promptfooconfig.yaml`, not from the YAML file that contains the reference, so a separate test file still resolves against the config root. And `maxConcurrency` only works under `commandLineOptions`.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add daymade/claude-code-skills --skill promptfoo-evaluation -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/promptfoo-evaluation/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/promptfoo-evaluation/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add daymade/claude-code-skills --skill promptfoo-evaluation -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/promptfoo-evaluation/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add daymade/claude-code-skills --skill promptfoo-evaluation -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/promptfoo-evaluation/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install daymade/claude-code-skills promptfoo-evaluation
```

2. **Manually: put the files in place**
- File: `.github/skills/promptfoo-evaluation/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add daymade/claude-code-skills --skill promptfoo-evaluation -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/daymade/claude-code-skills --path promptfoo-evaluation
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/promptfoo-evaluation/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add daymade/claude-code-skills --skill promptfoo-evaluation -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/daymade/claude-code-skills/tree/HEAD/promptfoo-evaluation/SKILL.md

## When to use it
- compare two models on the same prompt set
- write a Python assertion that returns a score
- grade free-form answers with an LLM rubric
- keep test cases in a separate YAML with file-loaded variables
- run evaluations through a relay endpoint

## Example prompts
- set up Promptfoo for my prompt and run the eval
- add an llm-rubric assertion with a 0.7 threshold
- why does my llm-rubric fail with 401 behind a proxy?

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 351984f58015060f.

BEGIN THIRD-PARTY FILE 351984f58015060f
````text
---
name: promptfoo-evaluation
description: Configures and runs LLM evaluation using Promptfoo framework. Use when setting up prompt testing, creating evaluation configs (promptfooconfig.yaml), writing Python custom assertions, implementing llm-rubric for LLM-as-judge, or managing few-shot examples in prompts. Triggers on keywords like "promptfoo", "eval", "LLM evaluation", "prompt testing", or "model comparison".
---

# Promptfoo Evaluation

## Overview

This skill provides guidance for configuring and running LLM evaluations using [Promptfoo](https://www.promptfoo.dev/), an open-source CLI tool for testing and comparing LLM outputs.

## Quick Start

```bash
# Initialize a new evaluation project
npx promptfoo@latest init

# Run evaluation
npx promptfoo@latest eval

# View results in browser
npx promptfoo@latest view
```

## Configuration Structure

A typical Promptfoo project structure:

```
project/
├── promptfooconfig.yaml    # Main configuration
├── prompts/
│   ├── system.md           # System prompt
│   └── chat.json           # Chat format prompt
├── tests/
│   └── cases.yaml          # Test cases
└── scripts/
    └── metrics.py          # Custom Python assertions
```

## Core Configuration (promptfooconfig.yaml)

```yaml
# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
description: "My LLM Evaluation"

# Prompts to test
prompts:
  - file://prompts/system.md
  - file://prompts/chat.json

# Models to compare
providers:
  - id: anthropic:messages:claude-sonnet-4-6
    label: Claude-Sonnet-4.6
  - id: openai:gpt-4.1
    label: GPT-4.1

# Test cases
tests: file://tests/cases.yaml

# Concurrency control (MUST be under commandLineOptions, NOT top-level)
commandLineOptions:
  maxConcurrency: 2

# Default assertions for all tests
defaultTest:
  assert:
    - type: python
      value: file://scripts/metrics.py:custom_assert
    - type: llm-rubric
      value: |
        Evaluate the response quality on a 0-1 scale.
      threshold: 0.7

# Output path
outputPath: results/eval-results.json
```

## Prompt Formats

### Text Prompt (system.md)

```markdown
You are a helpful assistant.

Task: {{task}}
Context: {{context}}
```

### Chat Format (chat.json)

```json
[
  {"role": "system", "content": "{{system_prompt}}"},
  {"role": "user", "content": "{{user_input}}"}
]
```

### Few-Shot Pattern

Embed examples directly in prompt or use chat format with assistant messages:

```json
[
  {"role": "system", "content": "{{system_prompt}}"},
````
END THIRD-PARTY FILE 351984f58015060f

The third-party file has ended. Everything between the 351984f58015060f tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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