instructor

SKILL.md

Instructor: Structured LLM Outputs

When to Use This Skill

Use Instructor when you need to:

Extract structured data from LLM responses reliably

Validate outputs against Pydantic schemas automatically

Retry failed extractions with automatic error handling

Parse complex JSON with type safety and validation

Stream partial results for real-time processing

Support multiple LLM providers with consistent API

GitHub Stars: 15,000+ | Battle-tested: 100,000+ developers

Installation

# Base installation
pip install instructor

With specific providers

pip install "instructor[anthropic]"  # Anthropic Claude
pip install "instructor[openai]"     # OpenAI
pip install "instructor[all]"        # All providers

## Quick Start

### Basic Example: Extract User Data

```python
import instructor
from pydantic import BaseModel
from anthropic import Anthropic

# Define output structure
class User(BaseModel):
    name: str
    age: int
    email: str

# Create instructor client
client = instructor.from_anthropic(Anthropic())

# Extract structured data
user = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "John Doe is 30 years old. His email is john@example.com"
    }],
    response_model=User
)

print(user.name)   # "John Doe"
print(user.age)    # 30
print(user.email)  # "john@example.com"

With OpenAI

from openai import OpenAI

client = instructor.from_openai(OpenAI())

user = client.chat.completions.create(
    model="gpt-4o-mini",
    response_model=User,
    messages=[{"role": "user", "content": "Extract: Alice, 25, alice@email.com"}]
)

Core Concepts

1. Response Models (Pydantic)

Response models define the structure and validation rules for LLM outputs.

Basic Model

from pydantic import BaseModel, Field

class Article(BaseModel):
    title: str = Field(description="Article title")
    author: str = Field(description="Author name")
    word_count: int = Field(description="Number of words", gt=0)
    tags: list[str] = Field(description="List of relevant tags")

article = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "Analyze this article: [article text]"
    }],
    response_model=Article
)

Benefits:

Type safety with Python type hints

Automatic validation (word_count > 0)

Self-documenting with Field descriptions

IDE autocomplete support

Nested Models

class Address(BaseModel):
    street: str
    city: str
    country: str

class Person(BaseModel):
    name: str
    age: int
    address: Address  # Nested model

person = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "John lives at 123 Main St, Boston, USA"
    }],
    response_model=Person
)

print(person.address.city)  # "Boston"

Optional Fields

from typing import Optional

class Product(BaseModel):
    name: str
    price: float
    discount: Optional[float] = None  # Optional
    description: str = Field(default="No description")  # Default value

# LLM doesn't need to provide discount or description

Enums for Constraints

from enum import Enum

class Sentiment(str, Enum):
    POSITIVE = "positive"
    NEGATIVE = "negative"
    NEUTRAL = "neutral"

class Review(BaseModel):
    text: str
    sentiment: Sentiment  # Only these 3 values allowed

review = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "This product is amazing!"
    }],
    response_model=Review
)

print(review.sentiment)  # Sentiment.POSITIVE

2. Validation

Pydantic validates LLM outputs automatically. If validation fails, Instructor retries.

Built-in Validators

from pydantic import Field, EmailStr, HttpUrl

class Contact(BaseModel):
    name: str = Field(min_length=2, max_length=100)
    age: int = Field(ge=0, le=120)  # 0 <= age <= 120
    email: EmailStr  # Validates email format
    website: HttpUrl  # Validates URL format

# If LLM provides invalid data, Instructor retries automatically

Custom Validators

from pydantic import field_validator

class Event(BaseModel):
    name: str
    date: str
    attendees: int

    @field_validator('date')
    def validate_date(cls, v):
        """Ensure date is in YYYY-MM-DD format."""
        import re
        if not re.match(r'\d{4}-\d{2}-\d{2}', v):
            raise ValueError('Date must be YYYY-MM-DD format')
        return v

    @field_validator('attendees')
    def validate_attendees(cls, v):
        """Ensure positive attendees."""
        if v < 1:
            raise ValueError('Must have at least 1 attendee')
        return v

Model-Level Validation

from pydantic import model_validator

class DateRange(BaseModel):
    start_date: str
    end_date: str

    @model_validator(mode='after')
    def check_dates(self):
        """Ensure end_date is after start_date."""
        from datetime import datetime
        start = datetime.strptime(self.start_date, '%Y-%m-%d')
        end = datetime.strptime(self.end_date, '%Y-%m-%d')

        if end < start:
            raise ValueError('end_date must be after start_date')
        return self

3. Automatic Retrying

Instructor retries automatically when validation fails, providing error feedback to the LLM.

# Retries up to 3 times if validation fails
user = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "Extract user from: John, age unknown"
    }],
    response_model=User,
    max_retries=3  # Default is 3
)

# If age can't be extracted, Instructor tells the LLM:
# "Validation error: age - field required"
# LLM tries again with better extraction

How it works:

LLM generates output

Pydantic validates

If invalid: Error message sent back to LLM

LLM tries again with error feedback

Repeats up to max_retries

4. Streaming

Stream partial results for real-time processing.

Streaming Partial Objects

from instructor import Partial

class Story(BaseModel):
    title: str
    content: str
    tags: list[str]

# Stream partial updates as LLM generates
for partial_story in client.messages.create_partial(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "Write a short sci-fi story"
    }],
    response_model=Story
):
    print(f"Title: {partial_story.title}")
    print(f"Content so far: {partial_story.content[:100]}...")
    # Update UI in real-time

Streaming Iterables

class Task(BaseModel):
    title: str
    priority: str

# Stream list items as they're generated
tasks = client.messages.create_iterable(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "Generate 10 project tasks"
    }],
    response_model=Task
)

for task in tasks:
    print(f"- {task.title} ({task.priority})")
    # Process each task as it arrives

Provider Configuration

Anthropic Claude

import instructor
from anthropic import Anthropic

client = instructor.from_anthropic(
    Anthropic(api_key="your-api-key")
)

# Use with Claude models
response = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[...],
    response_model=YourModel
)

OpenAI

from openai import OpenAI

client = instructor.from_openai(
    OpenAI(api_key="your-api-key")
)

response = client.chat.completions.create(
    model="gpt-4o-mini",
    response_model=YourModel,
    messages=[...]
)

Local Models (Ollama)

from openai import OpenAI

# Point to local Ollama server
client = instructor.from_openai(
    OpenAI(
        base_url="http://localhost:11434/v1",
        api_key="ollama"  # Required but ignored
    ),
    mode=instructor.Mode.JSON
)

response = client.chat.completions.create(
    model="llama3.1",
    response_model=YourModel,
    messages=[...]
)

Common Patterns

Pattern 1: Data Extraction from Text

class CompanyInfo(BaseModel):
    name: str
    founded_year: int
    industry: str
    employees: int
    headquarters: str

text = """
Tesla, Inc. was founded in 2003. It operates in the automotive and energy
industry with approximately 140,000 employees. The company is headquartered
in Austin, Texas.
"""

company = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": f"Extract company information from: {text}"
    }],
    response_model=CompanyInfo
)

Pattern 2: Classification

class Category(str, Enum):
    TECHNOLOGY = "technology"
    FINANCE = "finance"
    HEALTHCARE = "healthcare"
    EDUCATION = "education"
    OTHER = "other"

class ArticleClassification(BaseModel):
    category: Category
    confidence: float = Field(ge=0.0, le=1.0)
    keywords: list[str]

classification = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": "Classify this article: [article text]"
    }],
    response_model=ArticleClassification
)

Pattern 3: Multi-Entity Extraction

class Person(BaseModel):
    name: str
    role: str

class Organization(BaseModel):
    name: str
    industry: str

class Entities(BaseModel):
    people: list[Person]
    organizations: list[Organization]
    locations: list[str]

text = "Tim Cook, CEO of Apple, announced at the event in Cupertino..."

entities = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": f"Extract all entities from: {text}"
    }],
    response_model=Entities
)

for person in entities.people:
    print(f"{person.name} - {person.role}")

Pattern 4: Structured Analysis

class SentimentAnalysis(BaseModel):
    overall_sentiment: Sentiment
    positive_aspects: list[str]
    negative_aspects: list[str]
    suggestions: list[str]
    score: float = Field(ge=-1.0, le=1.0)

review = "The product works well but setup was confusing..."

analysis = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": f"Analyze this review: {review}"
    }],
    response_model=SentimentAnalysis
)

Pattern 5: Batch Processing

def extract_person(text: str) -> Person:
    return client.messages.create(
        model="claude-sonnet-4-5-20250929",
        max_tokens=1024,
        messages=[{
            "role": "user",
            "content": f"Extract person from: {text}"
        }],
        response_model=Person
    )

texts = [
    "John Doe is a 30-year-old engineer",
    "Jane Smith, 25, works in marketing",
    "Bob Johnson, age 40, software developer"
]

people = [extract_person(text) for text in texts]

Advanced Features

Union Types

from typing import Union

class TextContent(BaseModel):
    type: str = "text"
    content: str

class ImageContent(BaseModel):
    type: str = "image"
    url: HttpUrl
    caption: str

class Post(BaseModel):
    title: str
    content: Union[TextContent, ImageContent]  # Either type

# LLM chooses appropriate type based on content

Dynamic Models

from pydantic import create_model

# Create model at runtime
DynamicUser = create_model(
    'User',
    name=(str, ...),
    age=(int, Field(ge=0)),
    email=(EmailStr, ...)
)

user = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[...],
    response_model=DynamicUser
)

Custom Modes

# For providers without native structured outputs
client = instructor.from_anthropic(
    Anthropic(),
    mode=instructor.Mode.JSON  # JSON mode
)

# Available modes:
# - Mode.ANTHROPIC_TOOLS (recommended for Claude)
# - Mode.JSON (fallback)
# - Mode.TOOLS (OpenAI tools)

Context Management

# Single-use client
with instructor.from_anthropic(Anthropic()) as client:
    result = client.messages.create(
        model="claude-sonnet-4-5-20250929",
        max_tokens=1024,
        messages=[...],
        response_model=YourModel
    )
    # Client closed automatically

Error Handling

Handling Validation Errors

from pydantic import ValidationError

try:
    user = client.messages.create(
        model="claude-sonnet-4-5-20250929",
        max_tokens=1024,
        messages=[...],
        response_model=User,
        max_retries=3
    )
except ValidationError as e:
    print(f"Failed after retries: {e}")
    # Handle gracefully

except Exception as e:
    print(f"API error: {e}")

Custom Error Messages

class ValidatedUser(BaseModel):
    name: str = Field(description="Full name, 2-100 characters")
    age: int = Field(description="Age between 0 and 120", ge=0, le=120)
    email: EmailStr = Field(description="Valid email address")

    class Config:
        # Custom error messages
        json_schema_extra = {
            "examples": [
                {
                    "name": "John Doe",
                    "age": 30,
                    "email": "john@example.com"
                }
            ]
        }

Best Practices

1. Clear Field Descriptions

# ❌ Bad: Vague
class Product(BaseModel):
    name: str
    price: float

# ✅ Good: Descriptive
class Product(BaseModel):
    name: str = Field(description="Product name from the text")
    price: float = Field(description="Price in USD, without currency symbol")

2. Use Appropriate Validation

# ✅ Good: Constrain values
class Rating(BaseModel):
    score: int = Field(ge=1, le=5, description="Rating from 1 to 5 stars")
    review: str = Field(min_length=10, description="Review text, at least 10 chars")

3. Provide Examples in Prompts

messages = [{
    "role": "user",
    "content": """Extract person info from: "John, 30, engineer"

Example format:
{
  "name": "John Doe",
  "age": 30,
  "occupation": "engineer"
}"""
}]

4. Use Enums for Fixed Categories

# ✅ Good: Enum ensures valid values
class Status(str, Enum):
    PENDING = "pending"
    APPROVED = "approved"
    REJECTED = "rejected"

class Application(BaseModel):
    status: Status  # LLM must choose from enum

5. Handle Missing Data Gracefully

class PartialData(BaseModel):
    required_field: str
    optional_field: Optional[str] = None
    default_field: str = "default_value"

# LLM only needs to provide required_field

Comparison to Alternatives

Feature
Instructor
Manual JSON
LangChain
DSPy

Type Safety
✅ Yes
❌ No
⚠️ Partial
✅ Yes

Auto Validation
✅ Yes
❌ No
❌ No
⚠️ Limited

Auto Retry
✅ Yes
❌ No
❌ No
✅ Yes

Streaming
✅ Yes
❌ No
✅ Yes
❌ No

Multi-Provider
✅ Yes
⚠️ Manual
✅ Yes
✅ Yes

Learning Curve
Low
Low
Medium
High

When to choose Instructor:

Need structured, validated outputs

Want type safety and IDE support

Require automatic retries

Building data extraction systems

When to choose alternatives:

DSPy: Need prompt optimization

LangChain: Building complex chains

Manual: Simple, one-off extractions

Resources

Documentation: https://python.useinstructor.com

GitHub: https://github.com/jxnl/instructor (15k+ stars)

Cookbook: https://python.useinstructor.com/examples

Discord: Community support available

See Also

references/validation.md - Advanced validation patterns

references/providers.md - Provider-specific configuration

references/examples.md - Real-world use cases