🛡️ LLMShield

A lightweight, zero-dependency Python library for protecting PII in LLM interactions.

Designed for seamless integration into API-driven applications with minimal configuration.

Overview

LLMShield delivers reliable detection and protection of sensitive information in English in LLM interactions by automatically redacting PII before sending context to the underlying LLM provider SDK. LLMShield then restores the redacted PII from the response.

Key Features

Core Capabilities	Advanced Features
Zero Dependencies Pure Python implementation	Conversation Memory Multi-turn support with entity consistency
Entity Detection Automatic identification using multi-layered analysis	Streaming Support Real-time processing for streaming responses
Selective Protection Granular control over specific entity types	Performance Optimised Efficient architecture with intelligent caching
Universal Compatibility Works with major LLM providers	Ready for Production Reliable and secure for service integration

Installation

pip install llmshield

Quick Start

Provider Compatibility

LLMShield has been fully tested with these providers:

Provider	Status	Features
OpenAI Chat Completions API	Full Support	Chat, Structured Output, Streaming, Tools
Anthropic Messages API	Full Support	Chat, Structured Output, Streaming, Tools
Google Gemini API	Full Support	Chat, Structured Output, Streaming, Tools
Cohere Chat API	Full Support	Chat, Structured Output, Streaming, Tools
xAI Responses API	Full Support	Chat, Structured Output, Streaming, Tools
OpenAI Compatibility Standard	Full Support	Chat, Structured Output, Streaming, Tools

Note: Due to model behaviour differences, slight performance variations may occur. Tune parameters and PII filtration levels based on your requirements.

Basic Usage

from openai import OpenAI
from llmshield import LLMShield

# Initialise with any LLM provider
client = OpenAI(api_key="your-api-key")
shield = LLMShield(llm_func=client.chat.completions.create)

# Single request with automatic protection
messages = [
    {"role": "user", "content": "Draft an email to Sarah Johnson at sarah.j@techcorp.com"}
]
response = shield.ask(model="gpt-4", messages=messages)

# Multi-turn conversation with entity consistency
messages = [
    {"role": "user", "content": "I'm John Smith from DataCorp"},
    {"role": "assistant", "content": "Hello! How can I help you?"},
    {"role": "user", "content": "Email me at john@datacorp.com"}
]
response = shield.ask(model="gpt-4", messages=messages)

Streaming Support

messages = [
    {"role": "user", "content": "Generate a report about Jane Doe (jane@example.com)"}
]
response_stream = shield.ask(model="gpt-4", messages=messages, stream=True)

for chunk in response_stream:
    print(chunk, end="", flush=True)

Manual Protection (Advanced)

For custom LLM integrations:

shield = LLMShield()

# Protect sensitive information
cloaked_prompt, entity_map = shield.cloak(
    "Contact John Doe at john.doe@company.com or call +1-555-0123"
)
print(cloaked_prompt)
# Output: "Contact <PERSON_0> at <EMAIL_1> or call <PHONE_2>"

# Process with LLM
llm_response = your_llm_function(cloaked_prompt)

# Restore original entities
restored_response = shield.uncloak(llm_response, entity_map)

Important: Individual cloak() and uncloak() methods support single messages only and do not maintain conversation history. For multi-turn conversations with entity consistency across messages, use the ask() method.

Note: PII cloaking only applies to text-based inputs (str, list[str], and messages). Non-text inputs such as file paths, binary data, and Pydantic models are passed through to the LLM without cloaking, as PII detection requires scannable text content.

High-Level Data Flow

graph LR
    A["Raw Input<br/>'Contact Dr. Smith at smith@hospital.org'"] --> B["Entity Detection<br/>PERSON: Dr. Smith<br/>EMAIL: smith@hospital.org"]

    B --> C["PII Anonymisation<br/>'Contact <PERSON_0> at <EMAIL_1>'"]

    C --> D["LLM Processing<br/>Safe text sent to<br/>OpenAI, Claude, etc."]

    D --> E["Response Restoration<br/>Placeholders → Original PII"]

    E --> F["Protected Output<br/>'I'll help you contact Dr. Smith<br/>at smith@hospital.org'"]

    %% Styling
    classDef flowStyle fill:#f8f9fa,stroke:#495057,stroke-width:2px,color:#212529
    classDef detectionStyle fill:#e8f4f8,stroke:#0c63e4,stroke-width:2px,color:#212529
    classDef anonymisationStyle fill:#fff3cd,stroke:#856404,stroke-width:2px,color:#212529
    classDef llmStyle fill:#f0e6ff,stroke:#6f42c1,stroke-width:2px,color:#212529
    classDef restorationStyle fill:#d1ecf1,stroke:#0c5460,stroke-width:2px,color:#212529

    class A flowStyle
    class B detectionStyle
    class C anonymisationStyle
    class D llmStyle
    class E restorationStyle
    class F flowStyle

Under the Hood: System Architecture

graph LR
    subgraph Input ["Input Layer"]
        A["Textual Input<br/>Contains PII Entities"]
    end

    subgraph Detection ["Entity Detection Engine"]
        B["Configurable Waterfall Detection<br/>• Phase 1: Pattern Recognition (RegEx)<br/>• Phase 2: Numerical Validation (Luhn)<br/>• Phase 3: Linguistic Analysis (NLP)<br/>• Selective Type Filtering (EntityConfig)<br/>9 Entity Types: PERSON, ORGANISATION, EMAIL, etc."]
    end

    subgraph Cloaking ["Entity Anonymisation"]
        C["Classification & Tokenization<br/>PII → Typed Placeholders<br/>Deterministic Mapping<br/>Format: <TYPE_INDEX>"]
    end

    subgraph Provider ["LLM Provider Interface"]
        D["Provider-Agnostic API Gateway<br/>Supported: OpenAI, Anthropic Claude,<br/>Google Gemini, Azure OpenAI,<br/>AWS Bedrock, Custom Endpoints"]
    end

    subgraph Restoration ["Entity De-anonymisation"]
        E["Inverse Token Mapping<br/>Placeholder Detection<br/>Bidirectional Text Reconstruction<br/>Integrity Preservation"]
    end

    subgraph Output ["Output Layer"]
        F["Reconstructed Response<br/>Original PII Restored<br/>Stream-Compatible"]
    end

    subgraph Memory ["State Management System"]
        G["Singleton Dictionary Cache<br/>LRU Conversation Cache<br/>Hash-Based Entity Mapping<br/>O(1) Lookup Complexity<br/>95% Memory Reduction"]
    end

    %% Primary data flow
    A --> B
    B --> C
    C --> D
    D --> E
    E --> F

    %% State management interactions
    Memory -.->|"Read/Write<br/>Entity Maps"| C
    Memory -.->|"Consistency<br/>Validation"| E

    %% Styling
    classDef inputStyle fill:#f8f9fa,stroke:#495057,stroke-width:2px,color:#212529
    classDef detectionStyle fill:#e8f4f8,stroke:#0c63e4,stroke-width:2px,color:#212529
    classDef cloakingStyle fill:#fff3cd,stroke:#856404,stroke-width:2px,color:#212529
    classDef providerStyle fill:#f0e6ff,stroke:#6f42c1,stroke-width:2px,color:#212529
    classDef restorationStyle fill:#d1ecf1,stroke:#0c5460,stroke-width:2px,color:#212529
    classDef outputStyle fill:#d4edda,stroke:#155724,stroke-width:2px,color:#212529
    classDef memoryStyle fill:#f8d7da,stroke:#721c24,stroke-width:2px,color:#212529

    class A inputStyle
    class B detectionStyle
    class C cloakingStyle
    class D providerStyle
    class E restorationStyle
    class F outputStyle
    class G memoryStyle

Entity Detection

The library detects and protects the following entity types:

Entity Type	Examples	Placeholder Format
Person	John Doe, Dr. Smith	`<PERSON_0>`
Organisation	Acme Corp, NHS	`<ORGANISATION_0>`
Place	London, Main Street	`<PLACE_0>`
Email	user@domain.com	`<EMAIL_0>`
Phone	+1-555-0123	`<PHONE_0>`
URL	https://example.com	`<URL_0>`
Credit Card	4111-1111-1111-1111	`<CREDIT_CARD_0>`
IP Address	192.168.1.1	`<IP_ADDRESS_0>`

Built-in Memory for Multi-Turn Conversations

Note: LLMShield maintains entity consistency across conversation turns, ensuring the same person or organisation receives the same placeholder throughout the session. This memory is built-in with zero external dependencies.

sequenceDiagram
    participant User
    participant LLMShield
    participant LLM

    User->>LLMShield: "I'm John Doe from DataCorp"
    LLMShield->>LLM: "I'm <PERSON_0> from <ORGANISATION_1>"
    LLM->>User: "Hello John Doe! How can I help?"

    User->>LLMShield: "Email john.doe@datacorp.com"
    LLMShield->>LLM: "Email <EMAIL_2>"
    LLM->>User: "I'll send it to john.doe@datacorp.com"

Provider Setup Examples

OpenAI Configuration - Standard & Beta APIs with full feature support

from openai import OpenAI
import llmshield

# Configuration constants
OPENAI_API_KEY = "your-openai-api-key"
AI_MAX_RETRIES = 3
AI_TIMEOUT = 30.0
OPENAI_MODEL = "gpt-4o"

# Initialise OpenAI client
openai_client = OpenAI(
    api_key=OPENAI_API_KEY,
    max_retries=AI_MAX_RETRIES,
    timeout=AI_TIMEOUT,
)

# Standard Chat Completions API
openai_shield = llmshield.LLMShield(
    llm_func=openai_client.chat.completions.create
)

# Beta API with Structured Output
openai_beta_shield = llmshield.LLMShield(
    llm_func=openai_client.beta.chat.completions.parse
)

# Usage examples
messages = [
    {"role": "user", "content": "Draft email to john.doe@company.com about Q4 report"}
]

response = openai_shield.ask(model=OPENAI_MODEL, messages=messages)

# Streaming with protection
messages = [
    {"role": "user", "content": "Generate customer report for Alice Smith"}
]

for chunk in openai_shield.ask(model=OPENAI_MODEL, messages=messages, stream=True):
    print(chunk, end="", flush=True)

xAI Configuration - OpenAI-compatible with zero additional setup

from openai import OpenAI  # xAI uses OpenAI SDK
import llmshield

# Configuration constants
XAI_BASE_URL = "https://api.x.ai/v1"
XAI_API_KEY = "your-xai-api-key"
AI_MAX_RETRIES = 3
AI_TIMEOUT = 30.0
XAI_MODEL = "grok-beta"

# Initialise xAI client
xai_client = OpenAI(
    base_url=XAI_BASE_URL,
    api_key=XAI_API_KEY,
    max_retries=AI_MAX_RETRIES,
    timeout=AI_TIMEOUT,
)

# Create shield - identical to OpenAI setup
xai_shield = llmshield.LLMShield(
    llm_func=xai_client.chat.completions.create
)

# Usage with xAI models
messages = [
    {"role": "user", "content": "Analyse customer data: John Smith, john@company.com, +1-555-0123"}
]

response = xai_shield.ask(model=XAI_MODEL, messages=messages)

# Multi-turn conversations with entity consistency
messages = [
    {"role": "user", "content": "I'm Sarah Johnson from TechCorp"},
    {"role": "assistant", "content": "Hello! How can I help you?"},
    {"role": "user", "content": "Email me the report at sarah.j@techcorp.com"}
]

response = xai_shield.ask(model=XAI_MODEL, messages=messages)

Anthropic Configuration - Native Messages API with advanced tool support

from anthropic import Anthropic
import llmshield

# Configuration constants
ANTHROPIC_API_KEY = "your-anthropic-api-key"
AI_MAX_RETRIES = 3
AI_TIMEOUT = 30.0
ANTHROPIC_MODEL = "claude-3-5-sonnet-20241022"

# Initialise Anthropic client
anthropic_client = Anthropic(
    api_key=ANTHROPIC_API_KEY,
    max_retries=AI_MAX_RETRIES,
    timeout=AI_TIMEOUT,
)

# Create shield with Messages API
anthropic_shield = llmshield.LLMShield(
    llm_func=anthropic_client.messages.create
)

# Usage with Claude models
messages = [
    {"role": "user", "content": "Review customer info: Alice Cooper, alice@musiccorp.com"}
]

response = anthropic_shield.ask(model=ANTHROPIC_MODEL, messages=messages)

# Streaming support
messages = [
    {"role": "user", "content": "Generate report for client data"}
]

for chunk in anthropic_shield.ask(model=ANTHROPIC_MODEL, messages=messages, stream=True):
    print(chunk, end="", flush=True)

# Tool usage with PII protection
PHONE_TOOL_SCHEMA = {
    "name": "make_call",
    "description": "Make a phone call",
    "input_schema": {
        "type": "object",
        "properties": {"phone": {"type": "string"}},
        "required": ["phone"]
    }
}

messages = [
    {"role": "user", "content": "Call John Doe at +1-555-0123"}
]

response = anthropic_shield.ask(
    model=ANTHROPIC_MODEL,
    messages=messages,
    tools=[PHONE_TOOL_SCHEMA]
)

OpenAI-Compatible Providers - Universal setup for any OpenAI-compatible API

from openai import OpenAI
import llmshield

# Configuration constants - customize for your provider
PROVIDER_BASE_URL = "https://api.your-provider.com/v1"
PROVIDER_API_KEY = "your-provider-api-key"
AI_MAX_RETRIES = 3
AI_TIMEOUT = 30.0
PROVIDER_MODEL = "provider-specific-model"

# Generic OpenAI-compatible provider setup
compatible_client = OpenAI(
    base_url=PROVIDER_BASE_URL,
    api_key=PROVIDER_API_KEY,
    max_retries=AI_MAX_RETRIES,
    timeout=AI_TIMEOUT,
)

# Create shield - same interface for all providers
provider_shield = llmshield.LLMShield(
    llm_func=compatible_client.chat.completions.create
)

# Usage with any OpenAI-compatible provider
messages = [
    {"role": "user", "content": "Process data: Emma Wilson, emma@startup.io, 192.168.1.100"}
]

response = provider_shield.ask(model=PROVIDER_MODEL, messages=messages)

Compatible Providers Include:

Together AI • Fireworks AI • Anyscale • Replicate
Groq • Perplexity • DeepInfra • OpenRouter
Local deployments (Ollama, vLLM, etc.)

Zero Learning Curve: Same LLMShield interface works across all providers. Switch between OpenAI, xAI, Anthropic, and compatible providers without changing your code structure.

Configuration

Custom Delimiters

shield = LLMShield(
    start_delimiter='[[',
    end_delimiter=']]'
)
# Entities appear as [[PERSON_0]], [[EMAIL_1]], etc.

Conversation Caching

LLMShield implements an LRU (Least Recently Used) cache to maintain entity consistency across multi-turn conversations. The cache stores entity mappings for conversation histories, ensuring that all entities (persons, organisations, emails, phones, etc.) mentioned in different messages receive the same placeholders.

shield = LLMShield(
    llm_func=your_llm_function,
    max_cache_size=10_000  # Default: 10,000
)

Cache Sizing Guidelines

Small Applications

< 1,000 concurrent conversations
max_cache_size=1000-5000
~500KB-1MB memory

Medium Applications

1,000-10,000 concurrent conversations
max_cache_size=5000-10000
~5MB-10MB memory

Large Applications

100,000 concurrent conversations
max_cache_size=50000-100000
~50MB-100MB memory

Memory Calculation: Each conversation stores a dictionary mapping PII entities to their placeholders. With an average of 20 PII entities per conversation, each cache entry uses approximately 1-2KB of memory (entity text + placeholder mappings + metadata).

Cache Strategy Decision Tree:

flowchart TD
    A[Cache Configuration] --> B{Concurrent conversations<br/>per worker?}

    B -->|< 10,000| C[Normal Cache<br/>max_cache_size: 10000<br/>Memory: ~10MB]
    B -->|10,000 - 50,000| D[Large Cache<br/>max_cache_size: 50000<br/>Memory: ~50MB]
    B -->|> 50,000| E[Enterprise Cache<br/>max_cache_size: 100000<br/>Memory: ~100MB]

    C --> F{Need user-specific<br/>caching?}
    D --> F
    E --> F

    F -->|No| G[Single LLMShield instance<br/>with chosen cache size]
    F -->|Yes| H[Multiple LLMShield instances<br/>partitioned by user type]

Per-Shield Caching Strategy:

Each LLMShield instance maintains its own independent cache, providing flexibility for:

Demographic Partitioning: Separate caches for different user types (premium vs. free, geographic regions, etc.)
Use Case Isolation: Different cache strategies for customer service vs. internal tools vs. public APIs
Memory Allocation: Distribute memory budgets across multiple shield instances based on priority
Custom Strategies: Implement specialized caching logic for specific workflows or data sensitivity levels

Cache Effectiveness Factors:

Short-lived workers: Cache benefits diminish with frequent recycling - prioritize memory efficiency
Long-lived workers: Larger caches significantly reduce "cold start" latency for entity detection
Worker density: Many workers sharing server resources require smaller per-worker caches
Traffic variability: Spiky loads benefit from larger caches to handle burst scenarios

Performance Impact: Cache hit rates above 80% significantly improve performance for multi-turn conversations by avoiding re-detection of previously seen entities. Size your cache based on expected concurrent "fresh" conversations that your server workers are actively serving, not total daily volume.

Selective PII Detection

New in v2.0+: LLMShield supports chaining for selective entity detection. This allows you to selectively disable specific types of PII protection based on your requirements while maintaining a clean, readable configuration.

Factory Methods for Common Configurations

from llmshield import LLMShield

# Opt-In: Enable ALL detection (including technical CONCEPTS like API/SQL)
shield = LLMShield.enable_all()

# Disable location-based entities (PLACE, IP_ADDRESS, URL)
shield = LLMShield.disable_locations()

# Baseline Chaining (Start with everything, then subtract)
shield = LLMShield.enable_all() \
            .without_locations() \
            .without_persons() \
            .without_concepts()

# Disable contact information (EMAIL, PHONE)
shield = LLMShield.disable_contacts()

# Enable only financial entities (CREDIT_CARD)
shield = LLMShield.only_financial()

Custom Entity Configuration

For fine-grained control, use the EntityConfig class:

from llmshield import LLMShield
from llmshield.entity_detector import EntityConfig, EntityType

# Create custom configuration
config = EntityConfig().with_disabled(
    EntityType.EMAIL,      # Disable email detection
    EntityType.PHONE,      # Disable phone detection
    EntityType.URL         # Disable URL detection
)

shield = LLMShield(entity_config=config)

# Or enable only specific types
config = EntityConfig().with_enabled(
    EntityType.PERSON,     # Only detect persons
    EntityType.CREDIT_CARD # Only detect credit cards
)

shield = LLMShield(entity_config=config)

Available Entity Types

All configurable entity types

EntityType.PERSON          # Names (John Doe, Dr. Smith)
EntityType.ORGANISATION    # Companies (Microsoft Corp)
EntityType.PLACE           # Locations (London, Main Street)
EntityType.EMAIL           # Email addresses
EntityType.PHONE           # Phone numbers
EntityType.URL             # Web addresses
EntityType.CREDIT_CARD     # Credit card numbers
EntityType.IP_ADDRESS      # IP addresses
EntityType.CONCEPT         # Technical acronyms (API, SQL) - [OPT-IN ONLY]

Note on CONCEPT Detection: In v2.0+, EntityType.CONCEPT is disabled by default to prevent false positives with technical documentation. Use .enable_all() or .with_enabled(EntityType.CONCEPT) to activate it.

Using Selective Detection with ask()

Selective detection works seamlessly with the ask() method for end-to-end protection:

from openai import OpenAI
from llmshield import LLMShield

client = OpenAI(api_key="your-api-key")

# Create shield that ignores URLs and IP addresses
shield = LLMShield.disable_locations(llm_func=client.chat.completions.create)

# This will protect names and emails but allow URLs through
messages = [
    {"role": "user", "content": "Contact John Doe at john@company.com or visit https://company.com"}
]
response = shield.ask(model="gpt-4", messages=messages)
# Cloaked: "Contact <PERSON_0> at <EMAIL_1> or visit https://company.com"

Performance Benefits

Selective detection can improve performance by:

Reducing detection overhead for unused entity types
Minimizing placeholder generation and entity mapping
Faster text processing with fewer regex operations

Recommended Configurations:

Customer service: Disable PLACE and URL if not handling location data
Financial applications: Use only_financial() for credit card protection only
Internal tools: Disable PERSON detection if processing system logs
Public APIs: Enable all types for maximum protection

Performance Impact:

Memory usage: 20-40% reduction
Processing speed: 15-30% improvement
Cache efficiency: Higher hit rates
Latency: Lower response times

Language Support

LLMShield currently supports English only with about ~95% accuracy. We plan to add support for other languages in the future.

Development

Setup

Requires uv for dependency management.

git clone https://github.com/brainpolo/llmshield.git
cd llmshield
uv sync

This creates a .venv/ with Python 3.14 and installs all dev dependencies.

Testing

# Run all tests
make tests

# Generate coverage report
make coverage

# Run linting and formatting
make ruff

# Check documentation coverage
make doc-coverage

Building and Publishing

# Build the package
make build

Publishing to PyPI (maintainers only)

Update version in pyproject.toml
Run quality checks:
```
make tests
make coverage
make ruff
```
Build and publish:
```
make build
uv run twine upload dist/*
```

Security Considerations

Security Aspect	Recommendation
Validation	Validate cloaked outputs before LLM transmission
Storage	Securely store entity mappings for persistent sessions
Delimiters	Choose delimiters that don't conflict with your data format
Input Validation	Implement comprehensive input validation
Auditing	Regularly audit entity detection accuracy

Contributing

We welcome contributions! Please see CONTRIBUTING.md for development guidelines and contribution process.

License

This project is licensed under the GNU Affero General Public License v3.0 - see LICENSE.txt for details.

Support

For questions, issues, or feature requests:

GitHub Issues: Report bugs or request features
Documentation: Full documentation
Community: Discussions and support

Maintainers

Aditya Dedhia (@adityadedhia)
Sebastian Andres (@S-andres0694)

Production Usage

LLMShield is used in production environments by brainful.one to protect user data confidentiality.

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.deepsource.toml		.deepsource.toml
.gitignore		.gitignore
.pre-commit-config.yaml		.pre-commit-config.yaml
.python-version		.python-version
CHANGELOG.md		CHANGELOG.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE.txt		LICENSE.txt
Makefile		Makefile
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🛡️ LLMShield

Overview

Key Features

Installation

Quick Start

Provider Compatibility

Basic Usage

Streaming Support

Manual Protection (Advanced)

High-Level Data Flow

Under the Hood: System Architecture

Entity Detection

Built-in Memory for Multi-Turn Conversations

Provider Setup Examples

Configuration

Custom Delimiters

Conversation Caching

Cache Sizing Guidelines

Selective PII Detection

Factory Methods for Common Configurations

Custom Entity Configuration

Available Entity Types

Using Selective Detection with ask()

Performance Benefits

Language Support

Development

Setup

Testing

Building and Publishing

Publishing to PyPI (maintainers only)

Security Considerations

Contributing

License

Support

Maintainers

Production Usage

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