🦍 ape

Your prompts, evolved. A CLI tool that uses LLMs to automatically improve your prompts — inspired by the Automatic Prompt Engineer (APE) paper.

"Large Language Models Are Human-Level Prompt Engineers" — Zhou et al., ICLR 2023

🐒 What is this?

ape takes a prompt you've written, generates multiple improved variants using an LLM, scores each variant on clarity, specificity, and effectiveness, then ranks them best-to-worst. It's the APE paper's generate → score → select pipeline in your terminal.

Three stages, two API calls:

1. 🧬 Generate — An LLM produces N improved variants of your prompt (high temperature for diversity)
2. 🏆 Score — The same LLM judges each variant on 3 criteria (low temperature for consistency)
3. 📊 Rank — Results sorted by overall score, displayed with color-coded ratings

The APE Connection

The original APE paper (Zhou et al., ICLR 2023) framed prompt optimization as natural language program synthesis — a black-box optimization problem where LLMs both propose candidate instructions and evaluate them. APE achieved human-level or better performance on 24/24 Instruction Induction tasks and famously discovered "Let's work this out in a step by step way to be sure we have the right answer" — beating the hand-crafted "Let's think step by step" CoT prompt.

This CLI implements a simplified version of that pipeline, adapted for interactive use. Instead of execution accuracy on test pairs, we use multi-criteria LLM-as-judge scoring — making it work for any prompt, not just those with known answers.

🦧 AI Skill Usage

This tool is designed to be invoked by AI agents as a prompt improvement skill. When an AI receives a user's prompt, it can shell out to improve it before responding:

# AI agent calls this, parses JSON, uses the top-ranked variant
echo "summarize this article for me" | ape --json --count 3

The --json flag outputs machine-readable results that an AI can parse to:

• Pick the highest-scoring variant as the improved prompt
• Present multiple options to the user for selection
• Explain why the improved prompt is better using the scoring criteria

Pipe-in, pipe-out, zero interactivity — a composable Unix tool for AI agent workflows.

🔧 Installation

Requires Bun runtime.

# Run directly without installing
bunx ape-cli --help

# Or install globally
bun install -g ape-cli

# Or clone and link locally
git clone https://github.com/kouryuu/ape-cli.git && cd ape-cli
bun install
bun link

Now you can use ape anywhere.

🚀 Usage

# Basic usage — pipe in a prompt
echo "Summarize this article" | ape

# Read from a file
cat prompt.txt | ape

# Generate 3 variants using Claude
echo "Write a poem about space" | ape --provider claude --count 3

# JSON output for scripting / AI skill usage
echo "Explain quantum computing" | ape --json

# Use with OpenRouter
echo "Help me debug" | ape --base-url https://openrouter.ai/api/v1 --model openai/gpt-4o

# Use with local Ollama
echo "Translate this" | ape --base-url http://localhost:11434/v1 --model llama3

# Extract just the top prompt
echo "My prompt" | ape --json | jq -r '.[0].text'

🏴‍☠️ Flags

| Flag | Default | Description | |------|---------|-------------| | --provider | auto-detect | openai or claude. Auto-detected from env vars. | | --model | gpt-4o-mini / claude-sonnet-4-20250514 | Model for generation and scoring | | --base-url | provider default | Override API base URL | | --count | 5 | Number of variants to generate | | --json | false | Machine-readable JSON output | | --help | — | Show usage |

🔑 Environment Variables

| Variable | Provider | Description | |----------|----------|-------------| | OPENAI_API_KEY | openai | OpenAI (or compatible) API key | | ANTHROPIC_API_KEY | claude | Anthropic Claude API key |

Auto-detection: If no --provider is specified, the CLI checks which key is set. If both are set, defaults to openai.

📦 Provider Compatibility

| Provider | --provider | --base-url | Notes | |----------|-------------|-------------|-------| | OpenAI | openai | (default) | Uses OPENAI_API_KEY | | Claude | claude | (default) | Uses ANTHROPIC_API_KEY | | OpenRouter | openai | https://openrouter.ai/api/v1 | Set OPENAI_API_KEY to your OpenRouter key | | Ollama | openai | http://localhost:11434/v1 | No API key needed (set dummy value) | | Any OpenAI-compatible | openai | <your-url> | Works with any compatible endpoint |

📋 Output Formats

Pretty Mode (default)

✦ Prompt Improver — 5 variants generated and scored

  #1  ██████████████████░░  8.7/10
  ┃ You are an expert summarizer. Given the following article, produce a...
  ┃
  ┃ Clarity: 9  Specificity: 8  Effectiveness: 9
  ┃ Feedback: Added role assignment and output format constraints
  ┃ Changes: Assigned expert role, added structured output requirement
  ┗━━━

JSON Mode (--json)

[
  {
    "rank": 1,
    "text": "You are an expert summarizer...",
    "reasoning": "Added role assignment and structured output",
    "scores": { "clarity": 9, "specificity": 8, "effectiveness": 9 },
    "overall": 8.7,
    "feedback": "Clear role and format guidance"
  }
]

🧪 Testing

bun test

Tests use mocked LLM providers — no API key required.

📜 Citation

This tool is inspired by:

@inproceedings{zhou2023large,
  title={Large Language Models are Human-Level Prompt Engineers},
  author={Zhou, Yongchao and Muresanu, Andrei Ioan and Han, Ziwen and Paster, Keiran and Pitis, Silviu and Chan, Harris and Ba, Jimmy},
  booktitle={ICLR},
  year={2023}
}

🦍 Zero Dependencies

This CLI has zero runtime dependencies. Everything is built on Bun built-ins:

• fetch for API calls
• Bun.stdin for input
• Bun.argv for arg parsing
• Raw ANSI escape codes for colors

Dev dependencies (typescript, @types/bun) are only used for type-checking.

📄 License

MIT © 2025 Rodrigo Reyes

Built with 🍌 by an ape who believes your prompts deserve better.