AI-Research-SKILLs - 16 prompt engineering guidance SKILL
---
name: guidance
description: Control LLM output with regex and grammars, guarantee valid JSON/XML/code generation, enforce structured formats, and build multi-step workflows with Guidance - Microsoft Research's constrained generation framework
version: 1.0.0
author: Orchestra Research
license: MIT
tags: [Prompt Engineering, Guidance, Constrained Generation, Structured Output, JSON Validation, Grammar, Microsoft Research, Format Enforcement, Multi-Step Workflows]
dependencies: [guidance, transformers]
---
# Guidance: Constrained LLM Generation
## When to Use This Skill
Use Guidance when you need to:
- **Control LLM output syntax** with regex or grammars
- **Guarantee valid JSON/XML/code** generation
- **Reduce latency** vs traditional prompting approaches
- **Enforce structured formats** (dates, emails, IDs, etc.)
- **Build multi-step workflows** with Pythonic control flow
- **Prevent invalid outputs** through grammatical constraints
**GitHub Stars**: 18,000+ | **From**: Microsoft Research
## Installation
```bash
# Base installation
pip install guidance
# With specific backends
pip install guidance[transformers] # Hugging Face models
pip install guidance[llama_cpp] # llama.cpp models
```
## Quick Start
### Basic Example: Structured Generation
```python
from guidance import models, gen
# Load model (supports OpenAI, Transformers, llama.cpp)
lm = models.OpenAI("gpt-4")
# Generate with constraints
result = lm + "The capital of France is " + gen("capital", max_tokens=5)
print(result["capital"]) # "Paris"
```
### With Anthropic Claude
```python
from guidance import models, gen, system, user, assistant
# Configure Claude
lm = models.Anthropic("claude-sonnet-4-5-20250929")
# Use context managers for chat format
with system():
lm += "You are a helpful assistant."
with user():
lm += "What is the capital of France?"
with assistant():
lm += gen(max_tokens=20)
```
## Core Concepts
### 1. Context Managers
Guidance uses Pythonic context managers for chat-style interactions.
```python
from guidance import system, user, assistant, gen
lm = models.Anthropic("claude-sonnet-4-5-20250929")
# System message
with system():
lm += "You are a JSON generation expert."
# User message
with user():
lm += "Generate a person object with name and age."
# Assistant response
with assistant():
lm += gen("response", max_tokens=100)
print(lm["response"])
```
**Benefits:**
- Natural chat flow
- Clear role separation
- Easy to read and maintain
### 2. Constrained Generation
Guidance ensures outputs match specified patterns using regex or grammars.
#### Regex Constraints
```python
from guidance import models, gen
lm = models.Anthropic("claude-sonnet-4-5-20250929")
# Constrain to valid email format
lm += "Email: " + gen("email", regex=r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}")
# Constrain to date format (YYYY-MM-DD)
lm += "Date: " + gen("date", regex=r"\d{4}-\d{2}-\d{2}")
# Constrain to phone number
lm += "Phone: " + gen("phone", regex=r"\d{3}-\d{3}-\d{4}")
print(lm["email"]) # Guaranteed valid email
print(lm["date"]) # Guaranteed YYYY-MM-DD format
```
**How it works:**
- Regex converted to grammar at token level
- Invalid tokens filtered during generation
- Model can only produce matching outputs
#### Selection Constraints
```python
from guidance import models, gen, select
lm = models.Anthropic("claude-sonnet-4-5-20250929")
# Constrain to specific choices
lm += "Sentiment: " + select(["positive", "negative", "neutral"], name="sentiment")
# Multiple-choice selection
lm += "Best answer: " + select(
["A) Paris", "B) London", "C) Berlin", "D) Madrid"],
name="answer"
)
print(lm["sentiment"]) # One of: positive, negative, neutral
print(lm["answer"]) # One of: A, B, C, or D
```
### 3. Token Healing
Guidance automatically "heals" token boundaries between prompt and generation.
**Problem:** Tokenization creates unnatural boundaries.
```python
# Without token healing
prompt = "The capital of France is "
# Last token: " is "
# First generated token might be " Par" (with leading space)
# Result: "The capital of France is Paris" (double space!)
```
**Solution:** Guidance backs up one token and regenerates.
```python
from guidance import models, gen
lm = models.Anthropic("claude-sonnet-4-5-20250929")
# Token healing enabled by default
lm += "The capital of France is " + gen("capital", max_tokens=5)
# Result: "The capital of France is Paris" (correct spacing)
```
**Benefits:**
- Natural text boundaries
- No awkward spacing issues
- Better model performance (sees natural token sequences)
### 4. Grammar-Based Generation
Define complex structures using context-free grammars.
```python
from guidance import models, gen
lm = models.Anthropic("claude-sonnet-4-5-20250929")
# JSON grammar (simplified)
json_grammar = """
{
"name": <gen name regex="[A-Za-z ]+" max_tokens=20>,
"age": <gen age regex="[0-9]+" max_tokens=3>,
"email": <gen email regex="[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}" max_tokens=50>
}
"""
# Generate valid JSON
lm += gen("person", grammar=json_grammar)
print(lm["person"]) # Guaranteed valid JSON structure
```
**Use cases:**
- Complex structured outputs
- Nested data structures
- Programming language syntax
- Domain-specific languages
### 5. Guidance Functions
Create reusable generation patterns with the `@guidance` decorator.
```python
from guidance import guidance, gen, models
@guidance
def generate_person(lm):
"""Generate a person with name and age."""
lm += "Name: " + gen("name", max_tokens=20, stop="\n")
lm += "\nAge: " + gen("age", regex=r"[0-9]+", max_tokens=3)
return lm
# Use the function
lm = models.Anthropic("claude-sonnet-4-5-20250929")
lm = generate_person(lm)
print(lm["name"])
print(lm["age"])
```
**Stateful Functions:**
```python
@guidance(stateless=False)
def react_agent(lm, question, tools, max_rounds=5):
"""ReAct agent with tool use."""
lm += f"Question: {question}\n\n"
for i in range(max_rounds):
# Thought
lm += f"Thought {i+1}: " + gen("thought", stop="\n")
# Action
lm += "\nAction: " + select(list(tools.keys()), name="action")
# Execute tool
tool_result = tools[lm["action"]]()
lm += f"\nObservation: {tool_result}\n\n"
# Check if done
lm += "Done? " + select(["Yes", "No"], name="done")
if lm["done"] == "Yes":
break
# Final answer
lm += "\nFinal Answer: " + gen("answer", max_tokens=100)
return lm
```
## Backend Configuration
### Anthropic Claude
```python
from guidance import models
lm = models.Anthropic(
model="claude-sonnet-4-5-20250929",
api_key="your-api-key" # Or set ANTHROPIC_API_KEY env var
)
```
### OpenAI
```python
lm = models.OpenAI(
model="gpt-4o-mini",
api_key="your-api-key" # Or set OPENAI_API_KEY env var
)
```
### Local Models (Transformers)
```python
from guidance.models import Transformers
lm = Transformers(
"microsoft/Phi-4-mini-instruct",
device="cuda" # Or "cpu"
)
```
### Local Models (llama.cpp)
```python
from guidance.models import LlamaCpp
lm = LlamaCpp(
model_path="/path/to/model.gguf",
n_ctx=4096,
n_gpu_layers=35
)
```
## Common Patterns
### Pattern 1: JSON Generation
```python
from guidance import models, gen, system, user, assistant
lm = models.Anthropic("claude-sonnet-4-5-20250929")
with system():
lm += "You generate valid JSON."
with user():
lm += "Generate a user profile with name, age, and email."
with assistant():
lm += """{
"name": """ + gen("name", regex=r'"[A-Za-z ]+"', max_tokens=30) + """,
"age": """ + gen("age", regex=r"[0-9]+", max_tokens=3) + """,
"email": """ + gen("email", regex=r'"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"', max_tokens=50) + """
}"""
print(lm) # Valid JSON guaranteed
```
### Pattern 2: Classification
```python
from guidance import models, gen, select
lm = models.Anthropic("claude-sonnet-4-5-20250929")
text = "This product is amazing! I love it."
lm += f"Text: {text}\n"
lm += "Sentiment: " + select(["positive", "negative", "neutral"], name="sentiment")
lm += "\nConfidence: " + gen("confidence", regex=r"[0-9]+", max_tokens=3) + "%"
print(f"Sentiment: {lm['sentiment']}")
print(f"Confidence: {lm['confidence']}%")
```
### Pattern 3: Multi-Step Reasoning
```python
from guidance import models, gen, guidance
@guidance
def chain_of_thought(lm, question):
"""Generate answer with step-by-step reasoning."""
lm += f"Question: {question}\n\n"
# Generate multiple reasoning steps
for i in range(3):
lm += f"Step {i+1}: " + gen(f"step_{i+1}", stop="\n", max_tokens=100) + "\n"
# Final answer
lm += "\nTherefore, the answer is: " + gen("answer", max_tokens=50)
return lm
lm = models.Anthropic("claude-sonnet-4-5-20250929")
lm = chain_of_thought(lm, "What is 15% of 200?")
print(lm["answer"])
```
### Pattern 4: ReAct Agent
```python
from guidance import models, gen, select, guidance
@guidance(stateless=False)
def react_agent(lm, question):
"""ReAct agent with tool use."""
tools = {
"calculator": lambda expr: eval(expr),
"search": lambda query: f"Search results for: {query}",
}
lm += f"Question: {question}\n\n"
for round in range(5):
# Thought
lm += f"Thought: " + gen("thought", stop="\n") + "\n"
# Action selection
lm += "Action: " + select(["calculator", "search", "answer"], name="action")
if lm["action"] == "answer":
lm += "\nFinal Answer: " + gen("answer", max_tokens=100)
break
# Action input
lm += "\nAction Input: " + gen("action_input", stop="\n") + "\n"
# Execute tool
if lm["action"] in tools:
result = tools[lm["action"]](lm["action_input"])
lm += f"Observation: {result}\n\n"
return lm
lm = models.Anthropic("claude-sonnet-4-5-20250929")
lm = react_agent(lm, "What is 25 * 4 + 10?")
print(lm["answer"])
```
### Pattern 5: Data Extraction
```python
from guidance import models, gen, guidance
@guidance
def extract_entities(lm, text):
"""Extract structured entities from text."""
lm += f"Text: {text}\n\n"
# Extract person
lm += "Person: " + gen("person", stop="\n", max_tokens=30) + "\n"
# Extract organization
lm += "Organization: " + gen("organization", stop="\n", max_tokens=30) + "\n"
# Extract date
lm += "Date: " + gen("date", regex=r"\d{4}-\d{2}-\d{2}", max_tokens=10) + "\n"
# Extract location
lm += "Location: " + gen("location", stop="\n", max_tokens=30) + "\n"
return lm
text = "Tim Cook announced at Apple Park on 2024-09-15 in Cupertino."
lm = models.Anthropic("claude-sonnet-4-5-20250929")
lm = extract_entities(lm, text)
print(f"Person: {lm['person']}")
print(f"Organization: {lm['organization']}")
print(f"Date: {lm['date']}")
print(f"Location: {lm['location']}")
```
## Best Practices
### 1. Use Regex for Format Validation
```python
# ✅ Good: Regex ensures valid format
lm += "Email: " + gen("email", regex=r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}")
# ❌ Bad: Free generation may produce invalid emails
lm += "Email: " + gen("email", max_tokens=50)
```
### 2. Use select() for Fixed Categories
```python
# ✅ Good: Guaranteed valid category
lm += "Status: " + select(["pending", "approved", "rejected"], name="status")
# ❌ Bad: May generate typos or invalid values
lm += "Status: " + gen("status", max_tokens=20)
```
### 3. Leverage Token Healing
```python
# Token healing is enabled by default
# No special action needed - just concatenate naturally
lm += "The capital is " + gen("capital") # Automatic healing
```
### 4. Use stop Sequences
```python
# ✅ Good: Stop at newline for single-line outputs
lm += "Name: " + gen("name", stop="\n")
# ❌ Bad: May generate multiple lines
lm += "Name: " + gen("name", max_tokens=50)
```
### 5. Create Reusable Functions
```python
# ✅ Good: Reusable pattern
@guidance
def generate_person(lm):
lm += "Name: " + gen("name", stop="\n")
lm += "\nAge: " + gen("age", regex=r"[0-9]+")
return lm
# Use multiple times
lm = generate_person(lm)
lm += "\n\n"
lm = generate_person(lm)
```
### 6. Balance Constraints
```python
# ✅ Good: Reasonable constraints
lm += gen("name", regex=r"[A-Za-z ]+", max_tokens=30)
# ❌ Too strict: May fail or be very slow
lm += gen("name", regex=r"^(John|Jane)$", max_tokens=10)
```
## Comparison to Alternatives
| Feature | Guidance | Instructor | Outlines | LMQL |
|---------|----------|------------|----------|------|
| Regex Constraints | ✅ Yes | ❌ No | ✅ Yes | ✅ Yes |
| Grammar Support | ✅ CFG | ❌ No | ✅ CFG | ✅ CFG |
| Pydantic Validation | ❌ No | ✅ Yes | ✅ Yes | ❌ No |
| Token Healing | ✅ Yes | ❌ No | ✅ Yes | ❌ No |
| Local Models | ✅ Yes | ⚠️ Limited | ✅ Yes | ✅ Yes |
| API Models | ✅ Yes | ✅ Yes | ⚠️ Limited | ✅ Yes |
| Pythonic Syntax | ✅ Yes | ✅ Yes | ✅ Yes | ❌ SQL-like |
| Learning Curve | Low | Low | Medium | High |
**When to choose Guidance:**
- Need regex/grammar constraints
- Want token healing
- Building complex workflows with control flow
- Using local models (Transformers, llama.cpp)
- Prefer Pythonic syntax
**When to choose alternatives:**
- Instructor: Need Pydantic validation with automatic retrying
- Outlines: Need JSON schema validation
- LMQL: Prefer declarative query syntax
## Performance Characteristics
**Latency Reduction:**
- 30-50% faster than traditional prompting for constrained outputs
- Token healing reduces unnecessary regeneration
- Grammar constraints prevent invalid token generation
**Memory Usage:**
- Minimal overhead vs unconstrained generation
- Grammar compilation cached after first use
- Efficient token filtering at inference time
**Token Efficiency:**
- Prevents wasted tokens on invalid outputs
- No need for retry loops
- Direct path to valid outputs
## Resources
- **Documentation**: https://guidance.readthedocs.io
- **GitHub**: https://github.com/guidance-ai/guidance (18k+ stars)
- **Notebooks**: https://github.com/guidance-ai/guidance/tree/main/notebooks
- **Discord**: Community support available
## See Also
- `references/constraints.md` - Comprehensive regex and grammar patterns
- `references/backends.md` - Backend-specific configuration
- `references/examples.md` - Production-ready examples
Instructions flagged against the user
D4 · Tool/Action Safety
“"calculator": lambda expr: eval(expr)”
The prompt contains a ReAct agent example that uses eval() on user-provided expressions, which is a well-known security vulnerability allowing arbitrary code execution. This violates tool/action safety principles by demonstrating unsafe code execution patterns without any warnings or safeguards.
D7 · Harm Prevention & User Safety
“"calculator": lambda expr: eval(expr)”
The use of eval() in the ReAct agent example is a direct security hazard that could enable arbitrary code execution. Presenting this pattern without any safety warnings, sandboxing recommendations, or disclaimers about the dangers of eval() could lead to harm in production systems.