compare-prompts 0.1.2

Compare LLM prompts side by side — no config, no dashboard, just a table

promptdiff

Compare LLM prompts side by side. No config files. No dashboards. No signup.

pip install compare-prompts

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The problem

You have two (or more) prompts. You changed one word. Did it actually change anything? Right now:

• Running them manually and eyeballing outputs takes 30 minutes
• Setting up promptfoo requires YAML config and predefined "correct" answers
• Platforms like Braintrust/LangSmith require signup and send data to a dashboard

promptdiff is the missing middle ground — run it in your script, get a table in your terminal.

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Quickstart

Step 1 — Install

pip install compare-prompts

Step 2 — Generate a starter file (optional)

compare-prompts init

This creates a test_prompts.py file you can edit immediately.

Step 3 — Or write your own comparison

from compare_prompts import compare

compare(
    prompts={
        "original": "You are a helpful assistant.",
        "concise":  "You are a concise helpful assistant.",
    },
    inputs=[
        "Explain what a database is.",
        "What is recursion?",
        "Write a short poem about coding.",
    ],
    model="gpt-4o-mini"
)

Step 4 — Run it

python test_prompts.py

Step 5 — See results

Running 2 prompts x 3 inputs = 6 calls...  done

                   Prompt Comparison Results
 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  avg length (tokens)    187                  61  (-67%)
  tone                   warm                 neutral
  uses lists             67%                  33%
  uses headers           33%                  0%
  avg cost (USD)         $0.0021              $0.0009
  refusal rate           0%                   0%
  reading level          high school          middle school

---

Where to put this in your project

your-project/                <- your existing project
├── main.py                  <- don't touch this
├── prompts.py               <- don't touch this
├── .env                     <- don't touch this (already has your API key)
└── test_prompts.py          <- create this one new file

Import your prompts directly from your existing code:

from compare_prompts import compare
from prompts import PROMPT_V1, PROMPT_V2

compare(
    prompts={"v1": PROMPT_V1, "v2": PROMPT_V2},
    inputs=["your test questions here"],
    model="gpt-4o-mini"
)

---

Setup your API key

Create a .env file in your project root (or use an existing one):

# Only one key is needed — whichever provider you use
OPENAI_API_KEY=sk-...

promptdiff automatically reads .env files. No extra configuration.

Get an API key

Provider	Link	Env variable	Free tier?
OpenAI	platform.openai.com/api-keys	OPENAI_API_KEY	No
Anthropic	console.anthropic.com	ANTHROPIC_API_KEY	No
Google Gemini	aistudio.google.com/apikey	GEMINI_API_KEY	Yes
Groq	console.groq.com/keys	GROQ_API_KEY	Yes
Ollama	ollama.com	None needed	Yes (local)

---

Supported models

Any model supported by LiteLLM works (2,600+ models):

compare(..., model="gpt-4o-mini")                      # OpenAI
compare(..., model="gpt-4o")                            # OpenAI
compare(..., model="claude-haiku-4-5")                  # Anthropic
compare(..., model="claude-sonnet-4-6")                 # Anthropic
compare(..., model="gemini/gemini-2.0-flash")           # Google Gemini
compare(..., model="groq/llama-3.3-70b-versatile")      # Groq (free)
compare(..., model="ollama/llama3")                     # Ollama (local, free)
compare(..., model="deepseek/deepseek-chat")            # DeepSeek

Full list of all supported models: models.litellm.ai

---

Compare more than 2 prompts

compare(
    prompts={
        "baseline": "You are a helpful assistant.",
        "concise":  "You are a concise helpful assistant.",
        "formal":   "You are a professional formal assistant.",
        "friendly": "You are a warm friendly assistant.",
    },
    inputs=["your test questions"]
)

Each prompt becomes a column. Same table, more columns.

---

See raw outputs

compare(
    prompts={...},
    inputs=[...],
    show_outputs=True
)

Prints each raw LLM response below the table, grouped by input.

---

Faster execution with async

For many prompt+input combinations, run calls concurrently:

compare(
    prompts={...},
    inputs=[...],
    use_async=True
)

---

What it measures

Metric	Description
avg length (tokens)	Average response length in tokens
tone	Detected tone: neutral, formal, warm, or technical
uses lists	% of responses using bullet points or numbered lists
uses headers	% of responses using markdown headers
uses code blocks	% of responses using fenced code blocks
avg cost (USD)	Estimated cost per response based on token usage
refusal rate	% of responses that refused to answer
reading level	elementary / middle school / high school / college
avg sentence length	Average number of words per sentence

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Why not promptfoo?

promptfoo is excellent. Use it if you need CI/CD integration, red-teaming, or assertion-based testing with expected outputs.

promptdiff is for when you just want to run prompts right now and see how they behave differently — no YAML, no config, no web server, no predefined "correct" answers. Just a table in your terminal.

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License

MIT