Praxis turns a schema + examples into an optimized LLM prompt. You define the task, Praxis finds the best prompt automatically using an agentic optimizer that diagnoses failures and iterates, and you get a portable model.config.json that works with any LLM.

Install

npm install @drawcall/praxis

Or add it as a skill for your coding agent (Claude Code, Cursor, Copilot, Codex, Gemini CLI, and more):

npx skills add drawcall-ai/praxis

Workflow: Define → Train (optional) → Build → Run

1. Define

Create model.definition.ts with a schema, examples, and a metric:

import { z } from 'zod';
import { defineModel } from '@drawcall/praxis';

export default defineModel({
  name: 'Sentiment Analyzer', // optional: human-readable label shown in the web UI
  student: 'google/gemini-3-flash-preview',
  version: '1.0', // optional: bump to trigger retraining when examples or metrics change
  teacher: 'google/gemini-3.1-pro-preview', // optional: stronger model used as the optimizer agent
  description: 'Classify product review sentiment with confidence.', // optional: task description

  input: z.object({
    reviewText: z.string().describe('The product review to analyze'),
  }),

  output: z.object({
    sentiment: z.enum(['positive', 'negative', 'neutral']),
    confidence: z.number().describe('Confidence score 0-1'),
  }),

  examples: [
    { input: { reviewText: 'Love this product!' }, output: { sentiment: 'positive', confidence: 0.95 } },
    { input: { reviewText: 'Terrible quality.' }, output: { sentiment: 'negative', confidence: 0.92 } },
    { input: { reviewText: 'It works fine.' }, output: { sentiment: 'neutral', confidence: 0.75 } },
    // ... at least 10 examples
  ],

  metric: ({ modelOutput, exampleOutput }) => {
    if (!exampleOutput) return null;
    return { accuracy: modelOutput.sentiment === exampleOutput.sentiment ? 1 : 0 };
  },
});

2. Train (optional)

npx praxis train

Auto-discovers model.definition.ts (or .js) anywhere in the project via glob, optimizes the prompt, and writes model.config.json next to the definition file. You can also pass an explicit path: npx praxis train -d path/to/model.definition.ts.

Training requires a metric and at least 10 examples — without it, Praxis generates a default instruction from the schema.

CLI options: --output, -o <path> · --force

Training parameters are configured in the definition:

export default defineModel({
  // ...
  split: [0.7, 0.15, 0.15], // train/val/test split (default: [0.7, 0.15, 0.15])
  targetScore: 0.9,    // target combined score on validation set (enables iterative optimization)
  maxIterations: 5,    // max optimization iterations when target not met (default: 5)
  maxTestsPerIteration: 100, // max example test runs the optimizer can use per iteration (default: 100)
});

Training is skipped if the config is already up to date. If version is set in the definition, schema/student/teacher changes without a version bump produce an error — bump the version to retrain.

How training works

The optimizer splits examples into train / val / test sets and runs an agentic loop powered by the teacher model (or student if no teacher is set). It:

Evaluates the default prompt on the validation set to establish a baseline
Tests subsets of training examples, inspects failing inputs and the target model's reasoning
Writes improved prompts that address the specific failure patterns it observes
After each iteration, evaluates on the validation set — if targetScore is set and not met, continues the conversation with the agent for up to maxIterations rounds
Selects the best prompt by validation score, then confirms on the held-out test set

A built-in tokenEfficiency metric (default weight 0.1) penalizes inference cost overhead — it compares the irreducible cost (user input + output) against actual cost (system prompt + thinking + output). The optimizer starts with maximum reasoning effort (xhigh) and finds the best quality/cost tradeoff.

The agent has full creative freedom over the system prompt — it can include step-by-step algorithms, few-shot examples, lookup tables, edge case warnings, and more.

3. Build

import { buildRequest } from '@drawcall/praxis';
import modelDefinition from './model.definition.js';
import modelConfig from './model.config.json'; // optional

const request = buildRequest(modelDefinition, { reviewText: '...' }, modelConfig);
// → { messages, schema, student, metric? }

4. Run

import { generateText } from '@drawcall/praxis';
import modelDefinition from './model.definition.js';

const { output, score } = await generateText({
  definition: modelDefinition,
  input: { reviewText: 'Amazing product!' },
});

Or from the CLI:

npx praxis run --reviewText "Great product!"

Multiple metrics

Return a Record<string, number> from metric to evaluate on multiple dimensions. Use optional metricWeights to control importance — if omitted, all metrics are weighted equally:

export default defineModel({
  student: 'google/gemini-3-flash-preview',

  input: z.object({
    reviewText: z.string().describe('The product review to evaluate'),
  }),

  output: z.object({
    quality: z.enum(['helpful', 'unhelpful']),
    sentiment: z.enum(['positive', 'negative', 'neutral']),
    hasSpecificDetails: z.boolean(),
  }),

  examples: [
    { input: { reviewText: 'Battery lasts 8 hours, charges in 30 min.' }, output: { quality: 'helpful', sentiment: 'positive', hasSpecificDetails: true } },
    { input: { reviewText: 'Bad.' }, output: { quality: 'unhelpful', sentiment: 'negative', hasSpecificDetails: false } },
    // ... at least 10 examples
  ],

  metric: ({ modelOutput, exampleOutput }) => {
    if (!exampleOutput) return null;
    return {
      quality: modelOutput.quality === exampleOutput.quality ? 1 : 0,
      sentiment: modelOutput.sentiment === exampleOutput.sentiment ? 1 : 0,
      details: modelOutput.hasSpecificDetails === exampleOutput.hasSpecificDetails ? 1 : 0,
    };
  },

  metricWeights: { quality: 0.5, sentiment: 0.3, details: 0.2 }, // optional
});

generateText returns per-metric scores:

const { output, score } = await generateText({
  definition: modelDefinition,
  input: { reviewText: '...' },
});
// score → { quality: 1, sentiment: 1, details: 0 }

Async examples

Examples can be an async function instead of a plain array — useful for loading from a database or generating synthetic data:

export default defineModel({
  student: 'google/gemini-3-flash-preview',

  input: z.object({ text: z.string() }),
  output: z.object({ label: z.enum(['a', 'b', 'c']) }),

  examples: async () => {
    const rows = await fetchTrainingData();
    return rows.map(r => ({ input: { text: r.text }, output: { label: r.label } }));
  },

  metric: ({ modelOutput, exampleOutput }) => {
    if (!exampleOutput) return null;
    return { accuracy: modelOutput.label === exampleOutput.label ? 1 : 0 };
  },
});

You can also use top-level await for simpler cases — no special syntax needed.

Versioning

The optional version field signals when to retrain. Schema, student, and teacher changes are detected automatically, but changes to metric logic or example content are not. Bump the version to trigger retraining:

export default defineModel({
  student: 'google/gemini-3-flash-preview',
  version: '1.1', // was '1.0' — bumped because metric changed

  // ...
});

If version is set and schema/student/teacher change without a version bump, praxis train errors — this prevents accidental drift. Use --force to bypass.

Examples without expected output

The output field on examples is optional. This is useful for metrics that evaluate the prediction on its own (e.g. length, format, safety) without comparing to a ground truth:

export default defineModel({
  student: 'google/gemini-3-flash-preview',

  input: z.object({ text: z.string() }),
  output: z.object({ summary: z.string() }),

  examples: [
    { input: { text: 'A long article about climate change...' } },
    { input: { text: 'Breaking news: new discovery in physics...' } },
  ],

  metric: ({ modelOutput }) => {
    return { quality: modelOutput.summary.length > 10 && modelOutput.summary.length < 200 ? 1 : 0 };
  },
});

If a metric returns null during training, Praxis throws an error — this usually means the metric expects exampleOutput but the examples don't provide it.

Runnable examples

See the examples/ directory for runnable projects:

sentiment — Single metric: classify review sentiment
review-quality — Multiple metrics: evaluate quality, sentiment, and detail

Run them:

pnpm install
pnpm --filter @drawcall/example-sentiment dev
pnpm --filter @drawcall/example-review-quality dev

CLI

Command	Description
`praxis train [-d <path>] [-f]`	Optimize prompts (auto-discovers definition via glob)
`praxis run [-d <path>] [-c <config>]`	Run inference (auto-discovers definition and config)
`praxis view [-d <path>] [-p <port>]`	Launch web UI to inspect eval runs and test manually
`praxis check [-d <path>] [-c <config>]`	Check config matches definition (schema, student, version, weights)

Features

Schema-driven — Define inputs and outputs with Zod, get type-safe results
Agentic optimization — An AI agent diagnoses failures, inspects model reasoning, and writes targeted prompt improvements
Iterative optimization — Set targetScore in the definition and the optimizer iterates up to N times, using a validation set for checkpoint selection
Token efficiency — Built-in metric penalizes reasoning cost overhead, pushing the optimizer to find the best quality/cost tradeoff
Portable output — model.config.json works with any LLM provider via OpenRouter
Works without training — Definitions alone produce results; training makes them better
Multi-metric with weights — Return a Record<string, number> with optional metricWeights for weighted optimization
Observable — Every optimizer step is logged: agent thinking, prompt iterations, model reasoning
CLI + code — Run from the terminal or import into your app
Agent-friendly — Install as a skill and let your coding agent write definitions

Requirements

Node.js >= 18
OPENROUTER_KEY in .env (openrouter.ai)

License

MIT

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Package last updated on 03 Apr 2026

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