pixie-qa 0.7.2

Automated quality assurance for AI applications

pixie-qa

Eval-driven development for Python LLM applications.

pixie-qa ships two complementary tools:

• eval-driven-dev agent skill — guides a coding agent through the full eval-driven development loop: instrument → capture → build dataset → test → investigate → iterate.
• pixie-qa Python package — the runtime: wrap() for data-boundary instrumentation, Runnable for dataset-driven test execution, built-in and custom evaluators, and the pixie CLI.

Agent Skill

Install

npx skills add yiouli/pixie-qa

Usage

Open a conversation with your coding agent and say something like:

"set up QA for my app"

The agent follows a six-step workflow:

1. Understand the app — entry point, execution flow, expected behaviors
2. Instrument with wrap() — mark data boundaries in the production code path
3. Define evaluators — map quality criteria to built-in or custom evaluators
4. Build a dataset — diverse representative scenarios in JSON
5. Run pixie test — real pass/fail scores for every scenario
6. Investigate & iterate — root-cause failures and fix

Python Package

Install

pip install pixie-qa
# with an LLM provider auto-instrumentor:
pip install "pixie-qa[openai]"   # openai | anthropic | langchain | google | dspy | all

wrap() — instrument data boundaries

Call wrap() at data boundaries in your application code. At test time, wrap(purpose="input") values are injected from the dataset; wrap(purpose="output") values are captured and scored by evaluators.

from pixie import wrap

db_result = wrap(fetch_from_db(user_id), purpose="input", name="db_result")
response   = wrap(generate_response(db_result), purpose="output", name="response")

Purpose	Meaning
"input"	External data fed into the LLM (injected at test time)
"output"	Final or intermediate output to evaluate
"state"	Intermediate state captured for debugging

Runnable — run the app against each dataset entry

Implement the Runnable protocol so pixie test and pixie trace know how to run your app:

from pydantic import BaseModel
import pixie

class MyArgs(BaseModel):
    user_id: str
    message: str

class MyAppRunnable(pixie.Runnable[MyArgs]):
    @classmethod
    def create(cls) -> "MyAppRunnable":
        return cls()

    async def setup(self) -> None:
        pass  # one-time initialization before entries run

    async def run(self, args: MyArgs) -> None:
        await my_app.handle(args.user_id, args.message)

    async def teardown(self) -> None:
        pass  # one-time cleanup after all entries finish

run() is called concurrently for all dataset entries — protect shared mutable state with asyncio.Semaphore or asyncio.Lock if needed.

Dataset JSON format

{
  "runnable": "pixie_qa/scripts/run_app.py:MyAppRunnable",
  "evaluators": ["Factuality"],
  "entries": [
    {
      "input_data": { "user_id": "u1", "message": "What is my balance?" },
      "test_case": {
        "eval_input": [
          {
            "purpose": "input",
            "name": "db_result",
            "data": { "balance": 120.5 }
          }
        ],
        "expectation": "Your current balance is $120.50.",
        "description": "basic balance query"
      }
    }
  ]
}

Use pixie trace + pixie format to capture real traces and turn them into dataset entries with the correct data shapes.

Evaluators

Evaluator	Task
Factuality	LLM-as-judge factual accuracy
ClosedQA	LLM-as-judge Q&A with reference answer
AnswerCorrectness	RAGAS combined factual + semantic similarity
EmbeddingSimilarity	Cosine similarity between output and expectation
ExactMatch	Deterministic exact string match
create_llm_evaluator	Custom prompt-based LLM-as-judge

Full evaluator list: docs/pixie/index.md

CLI reference

Command	Description
pixie test [path]	Run eval tests; open scorecard in browser
pixie trace --runnable R --input I --output O	Run a Runnable, capture trace to JSONL
pixie format --input I --output O	Convert a trace JSONL to a dataset entry JSON
pixie init [root]	Scaffold the pixie_qa/ working directory
pixie start [root]	Launch the web UI at http://localhost:7118

Web UI

View all eval artifacts (results, datasets, markdown docs) in a live-updating local web UI:

pixie start              # initializes pixie_qa/ (if needed) and opens http://localhost:7118
pixie start my_dir       # use a custom artifact root
pixie init               # scaffolds pixie_qa/ without starting the server

Changes to artifacts are pushed to the browser in real time via SSE.

Configuration

Pixie reads configuration from environment variables and a local .env file. Existing process env vars take priority over .env values.

Variable	Description
PIXIE_ROOT	Root directory for all generated artefacts
PIXIE_RATE_LIMIT_ENABLED	true to enable evaluator throttling
PIXIE_RATE_LIMIT_RPS	Max requests per second for LLM-as-judge calls
PIXIE_RATE_LIMIT_RPM	Max requests per minute
PIXIE_RATE_LIMIT_TPS	Max tokens per second
PIXIE_RATE_LIMIT_TPM	Max tokens per minute